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Review

Biosensors for Micro- and Nanoplastics Detection: A Review

by
Maria Daoutakou
and
Spyridon Kintzios
*
Laboratory of Cell Technology, Department of Biotechnology, Agricultural University of Athens, 11855 Athens, Greece
*
Author to whom correspondence should be addressed.
Chemosensors 2025, 13(4), 143; https://doi.org/10.3390/chemosensors13040143
Submission received: 25 March 2025 / Revised: 10 April 2025 / Accepted: 11 April 2025 / Published: 14 April 2025
(This article belongs to the Special Issue Sensors for Food Testing, Environmental Analysis, and Medical Diagnostics)
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Abstract

:
Microplastics (MPs) and nanoplastics (NPs), which are widespread in many habitats as the byproducts of various industrial processes, pose considerable environmental and health hazards. However, current, conventional methods for detecting and characterizing them are considerably lacking in throughput, sensitivity, reliability, and field deployability. In the current report, we review the state of the art in biosensor-based MP/NP detection, in particular, describing advances in optical and electrochemical approaches, along with the development of novel biorecognition elements and the application of bioinformatics tools.

1. Introduction

Plastics have become a crucial part of our everyday lives, bolstering a multitude of sectors such as healthcare, tourism, and various manufacturing industries. However, due to poor waste management systems, significant amounts of plastic waste find their way into landfills, water bodies, and other unregulated dumping sites. Microplastics (MPs) are defined as small plastic particles that are below 5 mm in length. Nanoplastics (NPs) are defined as plastics that measure from 1 nm to 1 µm in thickness. Large microplastics primarily result from the fragmentation of microfiber textiles, the disintegration of larger debris through microbial enzyme-mediated biodegradation and photo-oxidation, and wear and tear phenomena due to marine abrasion. Primary microplastics are manufactured for a specific purpose and are intentionally produced in small sizes. Examples include the microbeads used in personal care products, industrial abrasives, and pre-production plastic pellets. Secondary microplastics result from the fragmentation or breakdown of larger plastic items. This fragmentation occurs due to mechanical processes (e.g., sewage treatment or runoff), natural elements (e.g., sunlight or hydrodynamic processes), or biological processes. These processes cause larger plastic debris to degrade into smaller particles over time [1]. Small microplastics in the form of solid and liquid beads are used in personal care and beauty products, as well as scrubbing agents, spill clean-up products, and industrial abrasives (Figure 1). In the aquatic environment, near-anoxic digestion in sedimentary environments, photochemicals, biodegradation, and eco-weathering phenomena cause the release of submicroscopic to microscopic microplastics from disintegrating macroplastics [2,3,4,5].
Although microplastics are present in many habitats, their harmful ubiquity clearly represents damage to fauna and animals. Microplastics might obstruct the gut or vascular system of certain species. They can also act as endocrine disruptors. In either case, whether through their physical effects on wildlife or through chemical toxins, microplastics present a chemical danger to the environment, including the residues of antibiotics, toxic chemicals, and poisonous substances created by cyanobacteria [6,7,8]. These are ingested by organisms at the bottom of the food chain [9]. Under the action of enzymes within these organisms, harmful substances are released from the MPs. This ingestion and the subsequent release of harmful substances can lead to the bioaccumulation of MPs through the food chain, ultimately affecting the well-being of higher organisms, including humans [10,11,12].
Microplastics are also widely recognized as agents of toxicological effects, in particular aquatic organisms (Table 1). These range from hepatic steatosis (exhibited by Gammarus locusta) [13] and decreased gene expression linked to oxidative stress (observed in the livers of fish), through to decreased egg production, the reduction of hatching success, and abnormalities in embryos (as a consequence of egg exposure in fish and daphnia). The environmental hazards of microplastics include:
Pathogen Carriers: Depending on their size and density, MP aggregates may have a large surface area that can carry harmful pathogens [14].
Impact on Aquatic Life: Microplastics can attach to the intestinal tracts of fishes, causing intestinal flora imbalance, inflammation, and, potentially, death [15]. Smaller particles can accumulate in the gonads of fishes, reducing their fertility.
Food Chain Contamination: Floating microplastics are ingested by organisms at the bottom of the food chain, leading to the release of harmful substances and bioaccumulation throughout the food chain [16].
Human Health Risks: Microplastics have been found in human blood, placenta, and lungs. They can cause inflammation, infection, dizziness, difficulty in breathing, and even death, due to the pathogenic bacteria they carry [17,18,19].
Nanoplastics (NPs) pose higher ecological risks than microplastics (MPs), due to their smaller dimensions and colloidal properties, which increase their likelihood of being taken up by organisms and crossing biological barriers [20,21,22].
Table 1. Species that are most affected by microplastics: these species are particularly vulnerable due to their feeding strategies, habitat preferences, and physiological characteristics, making them important indicators of microplastic pollution in aquatic ecosystems. Biomolecules, whole cells or even organisms from these and other species may be used in developing novel biosensor principles and bioassays for MP detection.
Table 1. Species that are most affected by microplastics: these species are particularly vulnerable due to their feeding strategies, habitat preferences, and physiological characteristics, making them important indicators of microplastic pollution in aquatic ecosystems. Biomolecules, whole cells or even organisms from these and other species may be used in developing novel biosensor principles and bioassays for MP detection.
SpeciesImpact AssessmentReference
Invertebrates:
Daphnia magna (water flea)Frequently used in toxicity studies due to showing reduced growth, reproduction, and physiological changes [23]
Chironomus riparius (non-biting midge)Exhibits morphological deformities and reduced emergence rates [24]
Gammarus pulex (amphipod)Shows reduced assimilation efficiency and avoidance behavior toward microplastics[13]
Fish:
Danio rerio (zebrafish) Accumulates microplastics in the gills, gut, and liver, leading toinflammation and oxidative stress [25,26]
Rutilus rutilus (roach)Ingests microplastics, with larger females showing higher ingestion rates[27]
Micropterus salmoides (largemouth bass)Found to contain high concentrations of microplastics in closed lake ecosystems[28]
Amphibians:
Alytes obstetricans (common midwife toad)Tadpoles show bioaccumulation and mortality when exposed to microplastics[29]
Physalaemus cuvieri (South American frog)Tadpoles exhibit significant morphological and cytological changes due to microplastics exposure[30]
Microalgae and Cyanobacteria:
Chlamydomonas reinhardtiiShows reduced growth and photosynthetic efficiency when exposed to microplastics [31]
Microcystis aeruginosaExhibits increased toxin production and cell membrane damage[32]
Chlorella vulgarisShows reduced photosynthetic efficiency when exposed to MP leachates[33]
Most current methods for MP and NP detection are low in throughput, limiting their practical application for large-scale samples. In addition, samples such as soil and plant tissues are complex and require extensive pre-processing, which complicates the detection process, while environmental sampling conditions, such as the presence of organic matter and other contaminants, can interfere with the detection and characterization of MPs/NPs. In addition, current analytical tools may not be sensitive enough to detect and quantify the small sizes and low concentrations of microplastics in agricultural samples, while, at the same time, they are not portable, i.e., able to operate in the application field.
Biosensors offer a promising approach to developing methods and devices for detecting MPs and NPs, due to their high sensitivity and minimal requirements in terms of sample quantities. This is an important feature for MP detection because these particles are usually found in low concentrations and can be masked by other particles present in food and water samples. Furthermore, biosensors usually provide results within a very short time, another feature that is commonly referred to as time-reduction assays, which is beneficial when monitoring production chains or the environment. Additionally, these devices have the potential to be portable and could be used in the field, supporting continuous and real-time monitoring. Therefore, the objective of the present review is to review the current state of the art in detecting MPs and NPs using biosensor-based methods, along with a summary of the current, conventional approaches.

2. Conventional Methods for the Analysis of MPs and NPs

Microplastic detection methods can be broadly divided into established methods, which have been developed over decades, and emerging methodologies that offer a range of improvements. The established methods are widely described, and significant advances have been made in method development and automation. Conventional methods include visual sorting and Fourier transform infrared spectroscopy (FTIR), which, when used in tandem, could perpetuate the issue of false negatives, since visually undetectable MPs will score as an unknown false-negative fraction [34]. Microplastics exhibit physical diversity in size and shape, bringing associated difficulties in terms of representative sampling, reliable microplastic recovery from a complex matrix, and microplastic identification.

2.1. Visual Inspection and Microscopy

Microplastics were first reported in marine environments as early as 1969, using visual observation tools such as light microscopes. However, they were not confirmed to be microplastics until 2004, when FTIR was applied. The most widely agreed definition of microplastics is that they are particles of less than 5 mm in size. Consequently, the industry has become reliant on optical microscopy techniques for their detection [35]. This technique uses three basic steps, including sample enrichment and purity, accurate documentation of particles, and identification based on the experienced judgment of experts. This has been required in Europe since January 2022, following increased regulation [36]. There are a number of issues associated with visual counting and identification, due to subjective judgment and varied skill levels between individuals. Additionally, particles may be missed when looking for other preferred qualities that are not present in the particle. Sample preparation is extremely important for clarifying and separating the materials that are counted, especially with organic materials in water samples. The visualization of microplastics has now moved from light microscopy to more advanced techniques such as electron microscopy, which features better resolution and X-ray images of the ’inside’. The advantages of using electron microscopy for detecting and characterizing MPs and NPs include:
High Resolution: Electron microscopy provides extremely high resolution, allowing for the detailed visualization of very small particles, including NPs.
Detailed Morphology: Electron microscopy can reveal detailed information about the shape, size, and surface morphology of MP/NP particles.
Elemental Analysis: Techniques like scanning electron microscopy (SEM), combined with energy-dispersive X-ray spectroscopy (EDS), can provide elemental composition data, helping to identify the types of plastics found and any associated contaminants.
Versatility: Electron microscopy can be used to analyze a wide range of sample types, including environmental samples, plant tissues, and animal tissues.
Depth of Field: Electron microscopy offers a greater depth of field compared to optical microscopy, providing a more comprehensive view of the sample’s three-dimensional structure.

2.2. Spectroscopic Techniques

Spectroscopic techniques provide chemical fingerprints and have unparalleled capabilities for the identification of polymer types. Two spectroscopic techniques are routinely applied to microplastic analysis, including FTIR spectroscopy and Raman spectroscopy. The major advantages of these techniques are that they are non-destructive and that no special sample pretreatment is necessary. This allows the spectroscopic analysis of sample sizes that are in about the order of the microplastic size range. Unfortunately, no Raman techniques for particle analysis show a clear advantage for use in the detection of microplastic sizes of less than 100 μm [35]. In turn, the application of spectroscopic techniques for large particle analysis is limited by the time that is necessary for automated Raman measurements or low IR beam transmission through the particle. The interpretation of FTIR or Raman spectra is also very challenging because the spectra of different polymers have to be assigned correctly.
The possibility of advanced spectroscopic applications and the integration of spectroscopic analyses with other analytical techniques have been significant. Such strategies have been used, based on historical first advances in the utilization of nano-FTIR analysis for submicrometer microplastics. A disadvantage of spectroscopic analyses is the restricted quality of the analysis, which is sometimes caused by the low signal-to-noise ratio, especially with the limited size of the sample, and the limited microplastic detection size or spatial resolution with FTIR. Nevertheless, efforts have been made to develop methodologies that provide advanced counterpart analyses at the microplastic size, allowing for detailed imaging of particles through hyperspectral bioimaging. However, this research was conducted by comparing the analysis to other analytical techniques and databases as a means for cross-verification, and this protocol can be improved by updating the database [36,37,38,39,40].

2.3. Chromatographic Methods

Chromatography plays a vital role in the identification and quantification of MPs, mainly due to its superiority in the separation of different types of samples. Chromatographic methods are generally utilized in MP detection and analysis and comprise gas chromatography and liquid chromatography. Liquid chromatography can be further divided into high-performance liquid chromatography, ultra-performance liquid chromatography, and ion chromatography. In addition to separating organic from inorganic materials, both gas chromatography and liquid chromatography can effectively separate MPs from suspended particulate matter. Compared with the use of cellulose chromatography, extensive and further applications of chromatography, except HPTLC, in the analysis of MPs are urgently needed because new-generation MPs possess diverse ingredients that limit the efficiency of prior methods of sample separation [41,42,43].
The working principles of the main conventional methods for MP/NP detection are summarized in Table 2.

3. Biosensor-Based Methods for Microplastic Detection

Biosensors offer a novel approach to developing methods and devices for detecting microplastics (MP) because they present key benefits for this specific application. On the one hand, biosensors are well known for their high sensitivity and require minimal sample quantities of the target that is to be detected. This is an important feature for MP detection because these particles are usually found in low concentrations and can be masked by the other particles present in food and water samples. Furthermore, these devices usually provide results within a very short time, another feature that is commonly referred to as time-reduction assays, which is beneficial when monitoring production chains or the environment. Additionally, these devices have the potential to be portable and could be used in the field, supporting continuous and real-time monitoring. However, despite all these advantages, the development of biosensors that are capable of detecting MPs presents a series of technical constraints, difficulties, and research gaps that need to be resolved.
One research field that is yet to be thoroughly explored is the use of biosensors to detect and quantify MPs. This is because biosensors can offer certain advantages in terms of sensitivity, low detection limits, rapid response, portability, and potential field application. Also, these technologies offer the possibility of being low in cost and can offer environmentally friendly usage whenever bioanalysis is employed. The combination of a biological element that is capable of recognizing microplastics with a physical sensor gives rise to a biosensor, which represents an innovative tool for monitoring studies and the identification of product and process quality and control. However, the amount of research that has focused on using biosensor-based methods to detect the presence of microplastics (MP) in waters, soils, sediments, or other environments is currently limited in comparison with other detection techniques [44,45,46,47,48,49,50]. Various strategies have been used to develop biosensor-based detection techniques for MPs and NPs, including:
  • Development of Specific Recognition Elements: Creating antibodies, aptamers, and molecular imprinting polymers can enhance the specificity and rapid identification of MPs based on their shape, size, and polymer type.
  • Fluorescent Probes: Utilizing advanced fluorescent probes like Nile red and conjugated polymer nanoparticles (CPNs) can help in the rapid and selective detection of MPs. Improving the dyeing efficiency, reducing false positives through co-staining approaches, and a better understanding of fluorophore-plastic interactions are essential [51].
  • Surface-Enhanced Raman Scattering (SERS): Enhancing the Raman signal using gold or silver nanoparticles can improve the sensitivity of MP detection [52]. Combining SERS with machine learning models can further increase accuracy and speed [53].
  • Electrochemical Methods: Developing sensors based on electrochemical impedance spectroscopy (EIS) and other electrochemical techniques can provide the rapid and selective detection of MPs in various food matrices [54].
  • Artificial Intelligence (AI): Leveraging AI for automatic image processing, classification, and analysis of MPs can significantly enhance the efficiency and accuracy of detection methods [55].
In the following sections, these approaches will be presented in detail.

3.1. Receptor-Based Approaches

Bioreceptors like enzymes, antibodies, and nucleic acids are crucial for developing biosensors to detect MNPs, but specific receptors are challenging to find. The receptor-based detection of MPs and NPs offers several advantages over traditional methods. Receptors provide high specificity, allowing for the precise identification and differentiation of plastic types in environmental samples. This method can achieve a low limit of detection (LOD), which is crucial for environmental screening. Receptor-based detection can be miniaturized and automated, making it suitable for portable and handheld devices intended for field use. The receptors used in this approach include cells, proteins, peptides, fluorescent dyes, polymers, and micro/nanostructures, each offering unique benefits for detecting and identifying MPs and NPs.
The types of receptors used for micro/nanoplastic (MNP) detection include:
Cells (Bacteria): These can be genetically engineered to detect specific MNPs through biochemical reactions or changes in transducer signals [56].
Proteins (Antibodies, Enzymes, and Receptors): These biological molecules can bind to specific plastic-related chemicals or structures, providing high specificity [57]. In particular, short peptides can be designed to bind specifically to certain types of plastics. Peptides can also be immobilized on the surface of biosensors to create a functional layer that interacts with target MPs [58]. This functionalization enhances the biosensor’s ability to capture and detect specific proteins in a sample.
Fluorescent Dyes: Chemical compounds that emit light upon excitation and can stain plastics to enable detection through fluorescence microscopy or spectroscopy [59,60].
Polymers (Natural and Synthetic): These materials can interact with MNPs through electrostatic attractions or other mechanisms, leading to detectable changes [61].
Micro- and Nanostructures: These specially designed materials can capture and detect MNPs, due to their unique physical and chemical properties [62].
Gongi et al. [63] explored the use of extracellular polymeric substances (EPSs) derived from cyanobacteria as a sensitive membrane for detecting microplastics using electrochemical impedance spectroscopy (EIS). More analytically, they developed and characterized an EPS-based biosensor for detecting microplastics, focusing on polystyrene (PSS), polyamide (PA), polymethyl acrylate (PMA), and polyethylene (PE). For this purpose, EPSs were extracted from Gloeocapsa gelationosa, characterized, and then used to coat gold electrodes. EIS was employed to measure the interaction between EPSs and microplastics. Binding microplastics to the EPS membrane causes changes in the impedance, which are then recorded as Nyquist plots (Figure 2). These plots show the real and imaginary parts of the impedance, indicating the presence and concentration of microplastics. The EPS-based sensor demonstrated a low detection limit of 10−11 M for microplastics. The sensor’s performance varied with the size of the microplastics, with larger particles causing faster saturation. Challenges remained in terms of selectivity and the sensor’s practical application in complex environments.
Using another approach, Seggio et al. [64] developed a plasmonic gold nano-surface functionalized with an estrogen receptor (ER) for the rapid, quantitative, and highly sensitive detection of nanoplastics in seawater without sample pretreatments. The sensor required just 2 μL of sample, provided results in 3 min, and could detect nanoplastics in concentrations ranging from 1 to 100 ng/mL. The sensor’s performance was validated with real seawater samples from Naples, showing a concentration of ~30 ng/mL that was confirmed by conventional methods. The results of this study demonstrated the sensor’s high sensitivity, specificity, wide dynamic range, and potential for real-world applications in environmental monitoring. Of particular interest is the lack of prior labeling of the target molecules, thereby simplifying the detection process and reducing potential interference from labels, along with the sensor’s reusability, since it can be regenerated and reused multiple times, maintaining its performance over several cycles.
Xiao et al. [65] developed a photoelectrochemical (PEC) sensor for detecting microplastics in aquatic environments. The sensor leveraged the protein corona-induced aggregation effect (PCIAE) to detect polystyrene microplastics (PS-MPs) with high sensitivity and reproducibility. PCIAE is based on the strong adsorptive affinity between proteins, such as bovine serum albumin (BSA) and microplastics, due to hydrophobic interactions. BSA, being a single-chain polypeptide with a spherical structure, wraps around the MPs, forming a protein corona or crown-like shell, hence giving the name of the effect. In turn, the surfaces of MPs adsorbed with BSA have a different charge compared to surfaces not adsorbed with BSA (Figure 3). This creates a lack of homogeneity in the surface charge of the MPs, leading to an attractive patch-charge force. This force is the dominant factor that induces the rapid aggregation of PS MP-BSA conjugates in low-concentration salt solutions. This aggregation can be monitored by the PEC sensor to determine the concentration of MPs in the sample. Key features of the PCIAE/PEC sensor include a linear detection range of 0.5–500 μg/mL, a detection limit of 0.06 μg/mL, and a limit of quantification of 0.14 μg/mL. The sensor’s performance was validated through various tests, showing good stability, reproducibility, and real-time detection capabilities when using a digital multimeter (DMM) connected to a smartphone via Bluetooth. The developed PEC sensor offered a portable, cost-effective, and efficient solution for the in situ detection of MPs, with potential applications in environmental protection.

3.2. Optical Biosensors

Iri et al. [66] reported the development of a low-cost portable Raman spectrometer for the optical detection of microplastics in water, highlighting its design, functionality, and potential applications in environmental monitoring. Raman spectroscopy works in microplastic detection by utilizing the scattering of monochromatic light when it interacts with the molecules in a sample. Most of the light is absorbed or transmitted, but a small portion undergoes scattering. This scattering can be elastic (Rayleigh or Mie scattering) or inelastic (Raman scattering). In Raman scattering, the photons from the light source interact with the molecules, causing the electrons to jump into a virtual energy state. These electrons are unstable in this state and quickly fall back to a lower energy level, emitting photons in the process. The emitted photons have different energy levels compared to the incident photons, resulting in a change in frequency. The scattered light is filtered to block the Rayleigh scattered light and then diffracted to separate the different wavelengths. A CCD sensor captures the scattered light, which carries information about the molecular structure of the sample. The Raman spectrum obtained from the scattered light reveals peaks corresponding to the vibrational frequencies of the molecules. For microplastics, specific peaks in the Raman spectrum indicate the presence of specific chemical groups associated with plastic materials. The system developed in this research can detect microplastic concentrations as low as 0.015% w/v, with a linear detection range between 0.015% and 0.035% w/v and with signal saturation observed at concentrations around 0.075% w/v. Moreover, the device costs less than USD 370 and includes components such as a collimated laser, sample holder, notch filter, diffraction grating, and CCD sensor, all integrated into a 3D printed case.
Lee and Fang [67] also employed surface-enhanced Raman scattering (SERS) for the single-particle detection of submicroplastics. They demonstrated that gold nano-urchins (AuNUs) play a crucial role in SERS detection by serving as the SERS-active substrate. Their irregular spiky surface facilitates the formation of plasmonic “hotspots” upon aggregation, which significantly enhances the local electromagnetic field. This enhancement amplifies the Raman signals of certain analytes, such as polystyrene (PS) submicroplastics, making it possible to detect these particles at a single-particle level. The study found that the SERS of a single PS particle can be induced by as few as 1–5 particles of AuNUs, with an excitation wavelength of 785 nm being appropriate to match the red-shifted surface plasmon resonance of aggregated AuNUs.
Ahn et al. [68] reported the development of peptide-decorated microneedles for the rapid and selective detection of microplastics using Raman spectroscopy. Peptides play a crucial role in microplastic detection by providing specific binding affinities for different types of microplastics [69]. Due to their smaller size and greater environmental stability compared to antibodies, peptides are effective in overcoming the limitations of existing detection methodologies. In this particular study, peptides with specific amino acid sequences were immobilized onto microneedles embedded with gold nanorods, which facilitated the capture of microplastics. The peptides were modified with sulfhydryl (SH) groups at their termini to ensure efficient binding to the microneedle tips. This binding was confirmed through fluorescence imaging and Raman spectroscopy, demonstrating the successful attachment of microplastics to the microneedles. The use of peptides enhances the specificity and simplicity of microplastic capture, making them a potent solution for detecting microplastics in various environmental settings.
Following a different approach, Nozdriukhin et al. [70] developed a new type of optoacoustic imaging technique for tracking individual microparticles in vivo, specifically focusing on gold carbon-shell-coated silica-core microparticles for enhanced biomedical applications. Optoacoustic imaging, also known as photoacoustic imaging, works by combining optical and ultrasound techniques to visualize biological tissues. Short pulses of laser light are directed into the tissue. These pulses are typically in the near-infrared (NIR) range, which penetrates deeper into biological tissues and causes a rapid temperature rise, leading to thermal expansion. This, in turn, generates pressure waves (ultrasound waves), due to the thermoelastic effect. Ultrasound transducers placed on the tissue surface detect the generated ultrasound waves. These transducers convert the pressure waves into electrical signals, which are processed and reconstructed into images that represent the distribution of the absorbing molecules within the tissue. This reconstruction can be performed in two or three dimensions, providing detailed images of the tissue’s internal structures.
Optoacoustic imaging is particularly useful for visualizing blood vessels, detecting tumors, and tracking the distribution of contrast agents in vivo. It combines the high spatial resolution of ultrasound imaging with the high contrast of optical imaging, making it a powerful tool for biomedical applications. Gold-carbon shells provide several advantages in imaging, since the combination of carbon nanotubes (CNT) and gold nanoparticles (AuNP) in the shell structure significantly increases light absorption, particularly in the NIR range, which enhances the optoacoustic signal. In addition, the gold carbon shells help maintain the stability and monodispersity of the microparticles, preventing aggregation and ensuring smooth flow through the vascular network, which is crucial for accurate blood flow mapping and for avoiding tissue damage.
Rizzato et al. [71] optimized surface acoustic wave (SAW) sensors for detecting nanoplastics. SAWs are mechanical waves that travel along the surface of a piezoelectric material. SAWs are typically generated by applying an oscillating electrical potential to interdigital transducers (IDTs) on a piezoelectric substrate. The periodicity of the IDTs sets the SAW wavelength and determines the resonance frequency. Changes in the surface environment alter the transmitted signal, which can be measured in terms of amplitude and phase shifts. Their amplitude decays exponentially away from the surface, resulting in a penetration depth that is typically in the order of the acoustic wavelength (Figure 4). This strong localization makes SAWs highly sensitive to changes in the surface environment. The sensitivity of SAW sensors is enhanced by the fact that the mechanical excitation is localized near the surface. This makes them more responsive to small changes in mass or other surface properties, allowing for the detection of low-molecular-weight molecules and nanoparticles.
The advantages of using SAW sensors include:
  • High Sensitivity: SAW sensors exhibit high sensitivity, due to the strong localization of mechanical excitation in the surface region, making them more responsive to surrounding variations such as biorecognition events [72].
  • Miniaturization: These sensors can be miniaturized, allowing for portable and on-field applications; this is beneficial for environmental monitoring and precision agriculture [73].
  • Quick and Cheap Detection: The sensors provide rapid and cost-effective nanoplastic detection, which is useful for early diagnosis and monitoring campaigns [74].
  • Improved Performance: The optimized SAW sensors demonstrate better performance in terms of their sensitivity and limit of detection compared to other methods, such as electrochemical impedance sensors [75,76].
Figure 4 summarizes the working principle of a SAW biosensor for MPs.
These advantages make SAW sensors suitable for various applications, including environmental monitoring, biomedical diagnostics, and plant pathogen detection. The limit of detection (LOD) for polystyrene particles using SAW sensors in Ref. [71] was 0.3 ng. The SAW sensors were optimized for better performance by systematically changing the geometrical design parameters of the interdigital transducers (IDTs). Specifically, increasing the number of finger pairs from 20 to 80 improved the delay line transmission at the resonance frequency. The best-performing configuration was identified with Device D4, which had 80 finger pairs, a finger length of 1310 µm, an overlap length of 1200 µm, and an emitter–receiver distance of 2000 µm. This configuration provided the highest transmission and the sharpest resonance.
Surface plasmon resonance (SPR) biosensors have also been used for the determination of MPs at low concentrations. For example, Huang et al. [54] reported the use of estrogen receptors (ERs) that were able to bind with MPs, thereby affecting the retention time and detection rate in surface plasmon resonance (SPR) biosensors. The SPR device measures changes in the refraction angle as microplastics flow through a microfluidic channel. The interaction between microplastics and ERs causes changes in the SPR signal, which can then be quantified. Specifically, polystyrene (PS) microplastics, which have the largest surface charge, showed the longest retention time when interacting with ERs, indicating a higher binding force (Figure 5). The interaction between ERs and microplastics was verified using liquid chromatography and an ELISA-like method, demonstrating specificity and binding affinity. The dissociation rate constant (kd) was used to measure the binding force, with PS showing the highest affinity to ERs, followed by PVC and PE. In a similar approach, Arcadio et al. [77] reported the development of a highly sensitive optical biosensor for the rapid detection and quantification of nanoplastics in seawater, using a gold nanograting platform functionalized with estrogen receptors. The nanostructured grating (GNG) provided remarkable performance enhancements by extending the measurement range across five orders of magnitude. This was achieved through the excitation and mutual interaction of surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) phenomena occurring at the GNG chip. These hybrid plasmonic modes significantly improve binding sensitivity, allowing the detection of nanoplastics in concentrations ranging from 1 ng/mL to 100 ng/mL, which encompassed the expected environmental loads. The ER-GNG biosensor was tested on real seawater samples collected from the Naples area. The seawater samples were diluted to 1:20 with PBS to adjust the pH from > 8.0 to 7.4, ensuring the physiological pH for optimal interaction between the nanoplastics and the estrogen receptor. A sample volume of 2 μL was used for measurement, with an incubation time of 3 min. The plasmonic spectra were collected after washing with PBS. The concentration of nanoplastics in the real seawater sample was estimated to be approximately 30 ng/mL, based on the calibration curve. This result was confirmed using a conventional method involving filtration and evaporation, which estimated the concentration to be ~53 ng/mL, thereby demonstrating the validity of the ER-GNG sensor approach.

3.3. Electrochemical Biosensors

Electrochemical biosensors offer several advantages for the point-of-test detection of micro- and nanoplastics. In their recent review, de Sousa et al. [78] highlighted such advantages as portability, low cost, and rapid analysis. Electrochemical methods primarily involve amperometry and impedance analysis, using the following key electrochemical techniques:
1. Resistive pulse sensors—Tunable resistive pulse sensing (TRPS): This technique uses an elastomeric membrane that can be stretched to obtain the desired pore dimensions. When a particle passes through the aperture, it decreases the electrical current and produces a pulse that can be counted [79]. TRPS instruments can detect different sizes of particles in a polydispersive sample. This method is useful for analyzing particle size and concentration.
2. Electrochemical impedance, which includes the following:
Impedance flow cytometry (IFC) uses microelectrodes embedded inside a microchannel to perform single- or multiple-frequency analysis [80]. This method can detect, count, and analyze particles suspended in a flowing liquid. It provides a simple and label-free solution for many scenarios. IFC can be used to analyze microplastics in the size range of 300–1000 µm, and future research aims to extend the lower limit of size detection by optimizing channel and electrode dimensions.
- Graphene-based sensors: These sensors use electrochemical impedance spectroscopy (EIS) to detect microplastics. For example, a graphene electrode can be used to detect polystyrene microparticles by measuring impedance changes [54]. This method offers rapid results with minimal instrumentation and great simplicity. Baumgarten et al. [81] reported the development of a graphene gold nanoparticle-based bionanocomposite for the voltammetric detection of bisphenol in microplastics, highlighting its green synthesis and enhanced sensitivity for monitoring endocrine disruptors in the environment. Due to its content of various antioxidant compounds, guava (Psidium guajava) extract was used as a reducing agent to synthesize AuNPs and stabilize graphene.
These electrochemical methods are promising alternatives for microplastic detection due to their simplicity, rapid results, and potential for on-site analysis. Further research and validation are needed to fully establish the effectiveness of these methods for routine environmental monitoring.

3.4. Bioinformatic Approaches

Bergman et al. [82] developed an improved algorithm, PepBD, which can design peptides that bind to common plastics like polyethylene, polypropylene, polystyrene, and PET. These peptides have potential applications in microplastic pollution remediation, plastic-based biosensors, and the creation of antimicrobial surfaces. The new method shows promise in identifying high-affinity peptides, with better scores than previous designs. When a target protein binds to the peptide on the biosensor, it can induce a conformational change or other detectable signal. This signal can be transduced into an electrical, optical, or other measurable output, indicating the presence and concentration of the target protein.
This algorithm, PepBD, was developed by modifying an existing Monte Carlo-based method to design peptides that will bind to common plastics [83]. An ensemble of the different adsorbed conformations of a peptide on a plastic surface was used as the starting point for design, improving the sampling of the conformational space available to peptides. Simulated annealing was added to increase the sampling of the conformational and sequence space that was local to each starting peptide conformation.
The best designs of the plastic-binding peptides were enriched in amino acids with bulky sidechains, such as tryptophan, arginine, and histidine. These amino acids showed increased van der Waals interactions with the plastic surfaces. The peptides possessed patches of hydrophobic and hydrophilic amino acids. The location of these patches depended on the adsorbed conformation of the peptide. Hydrophobic patches were more likely to be in contact with the plastic surface, while hydrophilic patches were more likely to be solvent-exposed. The peptides typically had a mix of hydrophobic and hydrophilic amino acids, which helped to maintain their solubility in water and prevent aggregation.
In another approach, Jeon et al. [84] reported the development of a machine learning-integrated droplet microfluidic system for the efficient and accurate detection and classification of microplastics in environmental samples. The system, named MiDREAM, employed an optimized YOLO v8 model for the real-time detection, classification, and quantification of MPs, which were encapsulated into uniform droplets with a portable peristaltic pump and detected with a high-resolution CMOS sensor. With uniform droplet sizes, the concentration of MPs could be precisely measured, reducing the variability and improving the reliability of the results [85]. The MiDREAM system was tested on site at two locations with distinct environmental characteristics: the Han River in Seoul and the Yellow Sea, near Incheon in Korea. The system successfully captured MPs of various sizes and distributions under field conditions. The system maintained high detection accuracy across different water types, including deionized (DI), tap, river, and seawater samples. It achieved detection accuracies of 94.93% for DI water and 94.23% for tap water, with slightly lower accuracies in the river and seawater samples due to matrix interference.
A comparison of the basic performance of different biosensor technologies for MP/NP detection is given in the following Table 3. In order for the limits of detection of the different approaches to be comparable, MP molar concentrations were calculated on the basis of the molecular weight of styrene (104.15 g/mol).

4. Conclusions

There are several challenges in detecting MPs and NPs, which include a lack of standardized methods, low throughput, complex sample matrices, particle polydispersity, low sensitivity, environmental variability, and insufficient field deployability [86]. Addressing these challenges requires the development of novel analytical methods and sensors combining high-precision lab analysis with rapid onsite screening, thereby creating data hubs for future analysis. Biosensors, as a generic point-of-test approach, offer the capacity for rapid, high-throughput, and field-deployable methods for the onsite screening of MPs/NPs, which are currently lacking.
Among these biosensors, electrochemical biosensors are the least expensive and are highly sensitive to various analytes; they are typically fabricated strictly with commercialized materials. In contrast, optical and piezoelectric biosensors provide high sensitivity and selectivity. Both are potentially applicable for real-time monitoring as they are capable of remote monitoring without sample depletion. Although there are differences between the strategies applied to detect the MP samples and the aspects to be detected, all of these methods are rapid, accurate, and have the potential to be integrated with portable devices for on-site applications [87,88]. Based on the reported capacities and performances of biosensor technologies for MP detection so far, we feel that a combination of advanced electrochemical/bioelectrical assay techniques with microorganism membrane moieties (including whole cells), as well as using molecular imprinted polymers (MPIs) as a cost-efficient alternative to estrogen receptors, could lead to innovative biosensors being the future standard for MP analytics. By focusing on these strategies, rapid detection techniques for MPs can be significantly improved, making them more efficient, accurate, and practical for widespread use.
Of concern is the potential for false-positive results because of the presence in the samples of organic macromolecular components such as proteins, polysaccharides, and humic substances, which interfere with the detection and quantification of MPs. MPs can aggregate with microbial biomass or humic substances through hydrophobic interactions. Then, it is difficult to discriminate the MPs from the biological materials based only on their size. Another critical aspect is the limited stability of the biorecognition element when exposed to complex food and environmental matrices.
Despite these limitations, biosensors are the ideal solution for continuous monitoring to detect trends in contamination and to assess the effects of microplastics on biodiversity over a period of several years, representing an indispensable tool for planning long-term sustainable environmental strategies and practices. Future research may be focused on developing a low-cost, paper-based rapid test for MP/NP detection, which would facilitate the wide adoption of biosensors for environmental monitoring in this particular field of application.

Author Contributions

Conceptualization, M.D. and S.K.; methodology, M.D.; investigation, S.K.; writing—original draft preparation, M.D. and S.K.; writing—review and editing, S.K.; supervision, S.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Relative contribution (% of total production) of different plastics sources to annual microplastics production worldwide (data source: https://www.weforum.org/stories/2019/12/microplastics-ocean-plastic-pollution-research-salps/) (accessed on 13 December 2019).
Figure 1. Relative contribution (% of total production) of different plastics sources to annual microplastics production worldwide (data source: https://www.weforum.org/stories/2019/12/microplastics-ocean-plastic-pollution-research-salps/) (accessed on 13 December 2019).
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Figure 2. Schematic representation of the electrochemical impedance spectroscopy applied by Gongi et al. [63] for the detection of microplastics, using extracellular polymeric substances (EPSs) from cyanobacteria as the biorecognition elements. The EPSs were immobilized via spin-coating on the surface of the working electrode (PMA: polymethyl acrylate; PSS: polystyrene).
Figure 2. Schematic representation of the electrochemical impedance spectroscopy applied by Gongi et al. [63] for the detection of microplastics, using extracellular polymeric substances (EPSs) from cyanobacteria as the biorecognition elements. The EPSs were immobilized via spin-coating on the surface of the working electrode (PMA: polymethyl acrylate; PSS: polystyrene).
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Figure 3. Working principle of the photoelectrochemical (PEC) sensor for detecting microplastics that was reported by Xiao et al. [65]. The corona-shaped aggregates that form between polystyrene microplastics and bovine serum albumin (BSA) have a different charge compared to the surface not adsorbed by BSA, which, in turn, affects the current generated on the photoactive surface of the working electrode upon illumination.
Figure 3. Working principle of the photoelectrochemical (PEC) sensor for detecting microplastics that was reported by Xiao et al. [65]. The corona-shaped aggregates that form between polystyrene microplastics and bovine serum albumin (BSA) have a different charge compared to the surface not adsorbed by BSA, which, in turn, affects the current generated on the photoactive surface of the working electrode upon illumination.
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Figure 4. Schematic presentation of the working principle of a SAW biosensor for MP detection.
Figure 4. Schematic presentation of the working principle of a SAW biosensor for MP detection.
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Figure 5. Schematical demonstration of the working principle of an estrogen-receptor-based SPR-biosensor for MP determination according to Huang et al. [58].
Figure 5. Schematical demonstration of the working principle of an estrogen-receptor-based SPR-biosensor for MP determination according to Huang et al. [58].
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Table 2. Summary of main non-biosensing techniques for MP/NP detection.
Table 2. Summary of main non-biosensing techniques for MP/NP detection.
TechniqueWorking PrincipleStrengthsWeaknesses
Fourier transform infrared spectroscopy (FTIR)The basis of this technique is the Fourier-pair relationship between the interferogram (interference function) of a substance and its spectrum. Infrared light from the light source passes through a Michelson interferometer and is absorbed by the sample. The bonds between different atoms absorb light at different frequencies.-Νon-destructive technique.
-Simultaneous analysis can be performed for multiple compounds.
-High sensitivity.
-No calibration required.
-High resolution.		-Only functional groups in a sample may be identified, not individual molecules.
Electron microscopyA primary electron beam is brought into contact with the surface of the tested sample, creating several interactions (mainly X-ray), thereby generating information about the chemical and spatial distribution of MPs in the sample.-High resolution.
-Elemental analysis.
-Wide scope of samples.		-Expensive and sophisticated instrumentation.
-Need for an expert end-user.
-Lack of portability.
Pyrolysis gas chromatography–mass spectrometry (Py-GC-MS)MPs are pyrolyzed by controlled thermal degradation under an inert atmosphere. The resulting lower molecular-weight molecules are separated chromatographically by GC and detected through MS by their mass spectrum.-Reduced interference by MP characteristics (e.g., color, size, and shape) and/or additives.
-Small amount of sample required.		-Not suitable for highly complex and heterogeneous samples.
-Expensive and sophisticated instrumentation.
Table 3. Key performance indicators of selected biosensor technologies for MP/NP detection.
Table 3. Key performance indicators of selected biosensor technologies for MP/NP detection.
Type of AssayBiorecognition ElementSample TypeLOD *Reference
Electrochemical impedance spectrometry (EIS)Extracellular polymeric substances from the cyanobacterium G. gelationosaStandard solutions10−6 to 10−11 M[63]
GrapheneStandard solutions15 nM[81]
Surface-plasmon resonance (SPR)Estrogen receptorSeawater1 ng/mL[64,77]
Standard solutions0.09 nM[76]
Raman scattering-Standard solutions0.015% w/v[66]
MP-binding peptidesMice tissue extractsn/a[68]
Microfluidic CMOS sensor-Tap, river, and sea water0.01% w/v[84]
Photoelectrochemical (PEC)ProteinTap and river water60 ng/mL[65]
Surface acoustic wave (SAW) Estrogen receptorsStandard solutions0.3 ng/mL[71]
* Molar concentrations were calculated on the basis of the molecular weight of styrene (104.15 g/mol).
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Daoutakou, M.; Kintzios, S. Biosensors for Micro- and Nanoplastics Detection: A Review. Chemosensors 2025, 13, 143. https://doi.org/10.3390/chemosensors13040143

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Daoutakou M, Kintzios S. Biosensors for Micro- and Nanoplastics Detection: A Review. Chemosensors. 2025; 13(4):143. https://doi.org/10.3390/chemosensors13040143

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Daoutakou, Maria, and Spyridon Kintzios. 2025. "Biosensors for Micro- and Nanoplastics Detection: A Review" Chemosensors 13, no. 4: 143. https://doi.org/10.3390/chemosensors13040143

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Daoutakou, M., & Kintzios, S. (2025). Biosensors for Micro- and Nanoplastics Detection: A Review. Chemosensors, 13(4), 143. https://doi.org/10.3390/chemosensors13040143

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