Biosensors

Emotional stress negatively affects the quality of a person’s daily life. From a physiological point of view, stress is expressed in the excitation of the hypothalamic–pituitary–adrenal cortex axis, which leads to the release of the hormone cortisol into the blood. We developed a lateral flow immunoassay to detect cortisol in human salivary fluid and tested it on 10 healthy volunteers daily for about one month (n = 293 saliva samples). Cortisol was detected in concentrations ranging from 1 to 70 ng/mL. Salivary cortisol levels were confirmed by ELISA. The straightness range of LFIA calibration was from 1 to 100 ng/mL. The diagnostic sensitivity of the method was 73%. It was found that in 3 out of 10 subjects, fluctuations in the level of cortisol in saliva partially corresponded to the subjectively assessed level of stress. Full article

A regenerable bulk acoustic wave (BAW) biosensor is developed for the rapid, label-free and selective detection of Escherichia coli in liquid media. The geometry of the biosensor consists of a GaAs membrane coated with a thin film of piezoelectric ZnO on its top surface. A pair of electrodes deposited on the ZnO film allows the generation of BAWs by lateral field excitation. The back surface of the membrane is functionalized with alkanethiol self-assembled monolayers and antibodies against E. coli. The antibody immobilization was investigated as a function of the concentration of antibody suspensions, their pH and incubation time, designed to optimize the immunocapture of bacteria. The performance of the biosensor was evaluated by detection tests in different environments for bacterial suspensions ranging between 10³ and 10⁸ CFU/mL. A linear dependence between the frequency response and the logarithm of E. coli concentration was observed for suspensions ranging between 10³ and 10⁷ CFU/mL, with the limit of detection of the biosensor estimated at 10³ CFU/mL. The 5-fold regeneration and excellent selectivity towards E. coli detected at 10⁴ CFU/mL in a suspension tinted with Bacillus subtilis at 10⁶ CFU/mL illustrate the biosensor potential for the attractive operation in complex biological media. Full article

Recent years have witnessed an ever-increasing interest in developing electrochemical biosensors based on direct electron transfer-type bioelectrocatalysis. This work investigates the bioelectrocatalytic oxidation of glucose by membrane fractions of Gluconobacter oxydans cells on screen-printed electrodes modified with thermally expanded graphite and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Electrooxidation of glucose was shown to occur without the presence of electron transport mediators. Chronoamperometric and cyclic voltametric characteristics showed an increase of anodic currents at electrode potentials of 0–500 mV relative to the reference electrode (Ag/AgCl). The direct electron transfer effect was observed for non-modified PEDOT:PSS as well as for PEDOT:PSS linked with crosslinkers and conductive fillers such as polyethylene glycol diglycidyl or dimethyl sulfoxide. Bioelectrodes with this composite can be successfully used in fast reagent-free glucose biosensors. Full article

A middle ear infection is a prevalent inflammatory disease most common in the pediatric population, and its financial burden remains substantial. Current diagnostic methods are highly subjective, relying on visual cues gathered by an otoscope. To address this shortcoming, optical coherence tomography (OCT) has been integrated into a handheld imaging probe. This system can non-invasively and quantitatively assess middle ear effusions and identify the presence of bacterial biofilms in the middle ear cavity during ear infections. Furthermore, the complete OCT system is housed in a standard briefcase to maximize its portability as a diagnostic device. Nonetheless, interpreting OCT images of the middle ear more often requires expertise in OCT as well as middle ear infections, making it difficult for an untrained user to operate the system as an accurate stand-alone diagnostic tool in clinical settings. Here, we present a briefcase OCT system implemented with a real-time machine learning platform for middle ear infections. A random forest-based classifier can categorize images based on the presence of middle ear effusions and biofilms. This study demonstrates that our briefcase OCT system coupled with machine learning can provide user-invariant classification results of middle ear conditions, which may greatly improve the utility of this technology for the diagnosis and management of middle ear infections. Full article

The development of sensitive methods for the determination of potential bacterial contamination is of upmost importance for environmental monitoring and food safety. In this study, we present a new method combining a fast pre-enrichment step using a microporous cryogel and a detection and identification step using antimicrobial peptides (AMPs) and labelled antibodies, respectively. The experimental method consists of: (i) the capture of large amounts of bacteria from liquid samples by using a highly porous and functionalized cryogel; (ii) the detection and categorisation of Gram-positive and Gram-negative bacteria by determining their affinities toward a small set of AMPs; and (iii) the identification of the bacterial strain by using labelled detection antibodies. As proof of concept, the assessment of the three steps of the analysis was performed by using Escherichia coli and Bacillus sp. as models for Gram-negative and Gram-positive bacteria, respectively. The use of AMPs with broad specificity combined with labelled antibodies enabled the detection and potential categorization of a large spectrum of unknown or unexpected bacteria. Full article

Molecular diagnostics has been the front runner in the world’s response to the COVID-19 pandemic. Particularly, reverse transcriptase-polymerase chain reaction (RT-PCR) and the quantitative variant (qRT-PCR) have been the gold standard for COVID-19 diagnosis. However, faster antigen tests and other point-of-care (POC) devices have also played a significant role in containing the spread of SARS-CoV-2 by facilitating mass screening and delivering results in less time. Thus, despite the higher sensitivity and specificity of the RT-PCR assays, the impact of POC tests cannot be ignored. As a consequence, there has been an increased interest in the development of miniaturized, high-throughput, and automated PCR systems, many of which can be used at point-of-care. This review summarizes the recent advances in the development of miniaturized PCR systems with an emphasis on COVID-19 detection. The distinct features of digital PCR and electrochemical PCR are detailed along with the challenges. The potential of CRISPR/Cas technology for POC diagnostics is also highlighted. Commercial RT–PCR POC systems approved by various agencies for COVID-19 detection are discussed. Full article

Over the past few decades, a significant increase in multi-drug-resistant pathogenic microorganisms has been of great concern and directed the research subject to the challenges that the distribution of resistance genes represent. Globally, high levels of multi-drug resistance represent a significant health threat and there is a growing requirement of rapid, accurate, real-time detection which plays a key role in tracking of measures for the infections caused by these bacterial strains. It is also important to reduce transfer of resistance genes to new organisms. The, World Health Organization has informed that millions of deaths have been reported each year recently. To detect the resistant organisms traditional detection approaches face limitations, therefore, newly developed technologies are needed that are suitable to be used in large-scale applications. In the present study, the aim was to design a surface plasmon resonance (SPR) sensor with micro-contact imprinted sensor chips for the detection of Staphylococcus aureus. Whole cell imprinting was performed by N-methacryloyl-L-histidine methyl ester (MAH) under UV polymerization. Sensing experiments were done within a concentration range of 1.0 × 10²–2.0 × 10⁵ CFU/mL. The recognition of S. aureus was accomplished by the involvement of microcontact imprinting and optical sensor technology with a detection limit of 1.5 × 10³ CFU/mL. Selectivity of the generated sensor was evaluated through injections of competing bacterial strains. The responses for the different strains were compared to that of S. aureus. Besides, real experiments were performed with milk samples spiked with S. aureus and it was demonstrated that the prepared sensor platform was applicable for real samples. Full article

As an important DNA 3′-phosphatase, alkaline phosphatase can repair damaged DNA caused by replication and recombination. It is essential to measure the level of alkaline phosphatase to indicate some potential diseases, such as cancer, related to alkaline phosphatase. Here, we designed a simple and fast method to detect alkaline phosphatase quantitively. When alkaline phosphatase is present, the resulting poly T-DNA with a 3′-hydroxyl end was cleaved by exonuclease I, prohibiting the formation of fluorescent copper nanoparticles. However, the fluorescent copper nanoparticles can be monitored with the absence of alkaline phosphatase. Hence, we can detect alkaline phosphatase with this turn-off strategy. The proposed method is able to quantify the concentration of alkaline phosphatase with the LOD of 0.0098 U/L. Furthermore, we utilized this method to measure the effects of inhibitor Na₃VO₄ on alkaline phosphatase. In addition, it was successfully applied to quantify the level of alkaline phosphatase in human serum. The proposed strategy is sensitive, selective, cost effective, and timesaving, having a great potential to detect alkaline phosphatase quantitatively in clinical diagnosis. Full article

Organ-on-a-chip (OOC) devices offer new approaches for metabolic disease modeling and drug discovery by providing biologically relevant models of tissues and organs in vitro with a high degree of control over experimental variables for high-content screening applications. Yet, to fully exploit the potential of these platforms, there is a need to interface them with integrated non-labeled sensing modules, capable of monitoring, in situ, their biochemical response to external stimuli, such as stress or drugs. In order to meet this need, we aim here to develop an integrated technology based on coupling a localized surface plasmon resonance (LSPR) sensing module to an OOC device to monitor the insulin in situ secretion in pancreatic islets, a key physiological event that is usually perturbed in metabolic diseases such as type 2 diabetes (T2D). As a proof of concept, we developed a biomimetic islet-on-a-chip (IOC) device composed of mouse pancreatic islets hosted in a cellulose-based scaffold as a novel approach. The IOC was interfaced with a state-of-the-art on-chip LSPR sensing platform to monitor the in situ insulin secretion. The developed platform offers a powerful tool to enable the in situ response study of microtissues to external stimuli for applications such as a drug-screening platform for human models, bypassing animal testing. Full article

In recent years, Synthetic Biology has emerged as a new discipline where functions that were traditionally performed by electronic devices are replaced by “cellular devices”; genetically encoded circuits constructed of DNA that are built from biological parts (aka bio-parts). The cellular devices can be used for sensing and responding to natural and artificial signals. However, a major challenge in the field is that the crosstalk between many cellular signaling pathways use the same signaling endogenous molecules that can result in undesired activation. To overcome this problem, we utilized a specific promoter that can activate genes with a natural, non-toxic ligand at a highly-induced transcription level with low background or undesirable off-target expression. Here we used the orphan aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor that upon activation binds to specific AHR response elements (AHRE) of the Cytochrome P450, family 1, subfamily A, polypeptide 1 (CYP1A1) promoter. Flavonoids have been identified as AHR ligands. Data presented here show the successful creation of a synthetic gene “off” switch that can be monitored directly using an optical reporter gene. This is the first step towards bioengineering of a synthetic, nanoscale bio-part for constructing a sensor for molecular events. Full article

The plant cell mechanics, including turgor pressure and wall mechanical properties, not only determine the growth of plant cells, but also reflect the functional and structural changes of plant cells under biotic and abiotic stresses. However, there are currently no appropriate techniques allowing to monitor the complex mechanical properties of living plant cells non-invasively and continuously. In this work, quartz crystal microbalance with dissipation (QCM-D) monitoring technique with overtones (3–9) was used for the dynamic monitoring of adhesions of living tobacco BY-2 cells onto positively charged N,N-dimethyl-N-propenyl-2-propen-1-aminiumchloride homopolymer (PDADMAC)/SiO₂ QCM crystals under different concentrations of mannitol (C_M) and the subsequent effects of osmotic stresses. The cell viscoelastic index (CVI_n) (CVI_n = ΔD⋅n/ΔF) was used to characterize the viscoelastic properties of BY-2 cells under different osmotic conditions. Our results indicated that lower overtones of QCM could detect both the cell wall and cytoskeleton structures allowing the detection of plasmolysis phenomena; whereas higher overtones could only detect the cell wall’s mechanical properties. The QCM results were further discussed with the morphological changes of the BY-2 cells by an optical microscopy. The dynamic changes of cell’s generated forces or cellular structures of plant cells caused by external stimuli (or stresses) can be traced by non-destructive and dynamic monitoring of cells’ viscoelasticity, which provides a new way for the characterization and study of plant cells. QCM-D could map viscoelastic properties of different cellular structures in living cells and could be used as a new tool to test the mechanical properties of plant cells. Full article

The past decade has witnessed a surge into research on disruptive technologies that either challenge or complement conventional thoracic diagnostic modalities. The non-ionizing, non-invasive, compact, and low power requirements of electromagnetic (EM) techniques make them among the top contenders with varieties of proposed scanning systems, which can be used to detect wide range of thoracic illnesses. Different configurations, antenna topologies and detection or imaging algorithms are utilized in these systems. Hence, to appreciate their progress and assess their potential, a critical review of EM thoracic scanning systems is presented. Considering the numerous thoracic diseases, such as fatty liver disease, lung cancer, respiratory and heart related complications, this paper will exclusively focus on torso scanning systems, tracing the early foundation of research that studied the possibility of using EM waves to detect thoracic diseases besides exploring recent progresses. The advantages and disadvantages of proposed systems and future possibilities are thoroughly discussed. Full article

Human echinococcosis is a serious parasitic diseasethat still affects millions of people in many parts of the world. Since it can offer a critical threat to people’s health, it is important to discover a rapid, convenient, and economical method for detection. Herein, we propose a novel point of care assay, namely, an enhanced immuno-dot-blot assay for diagnosis of cystic echinococcosis (hydatidosis). This method is based on the formation of a sandwich complex between a goldnanoprobe (chitosan–gold nanoparticleprotein A) and hydatid cyst antigen (Ag B), which holds anti-Ag B antibodies. Briefly, protein A was conjugated to chitosan–gold nanoparticles via glutaraldehyde chemistry. Then, Ag B was immobilized on the surface of a nitrocellulose membrane, which was followed by the addition of the sera sample and gold nanoprobes. The positive signals were easily detectable by naked eye. The signal intensity of this biosensor was proportional to the concentration of active anti-Echinococcus granulosus antibodies on the surface of the nanoparticles, titer of antibodies in the sera samples, and concentration of Ag B coated on the nitrocellulose membrane. The minimum concentration to use the protein A for conjugation to detect titer of anti-Echinococcus IgGand the concentration of Ag B coated in nitrocellulose membrane were 0.5 and 0.3 mg/mL, respectively. This enhanced immuno-dot-blot assay offers a simple diagnostic technique withoutthe need for expensive equipment for diagnosis of echinococcosis. Full article

Analytical performance and efficiency are two pivotal issues for developing an on-site and real-time aptasensor for cadmium (Cd²⁺) determination. However, suffering from redundant preparations, fabrications, and incubation, most of them fail to well satisfy the requirements. In this work, we found that fluorescence intensity of 6-carboxyfluorescein(FAM)-labeled aptamer (FAM-aptamer) could be remarkably amplified by 3-(N-morpholino)propane sulfonic acid (MOPS), then fell proportionally as Cd²⁺ concentration introduced. Importantly, the fluorescence variation occurred immediately after addition of Cd²⁺, and would keep stable for at least 60 min. Based on the discovery, a facile and ultra-efficient aptasensor for Cd²⁺ determination was successfully developed. The sensing mechanism was confirmed by fluorescence pattern, circular dichroism (CD) and intermolecular interaction related to pK_a. Under the optimal conditions, Cd²⁺ could be determined rapidly from 5 to 4000 ng mL⁻¹. The detection limit (1.92 ng mL⁻¹) was also lower than the concentration limit for drinking water set by WHO and EPA (3 and 5 ng mL⁻¹, respectively). More than a widely used buffer, MOPS was firstly revealed to have fluorescence amplification effect on FAM-aptamer upon a given context. Despite being sensitive to pH, this simple, high-performance and ultra-efficient aptasensor would be practical for on-site and real-time monitoring of Cd²⁺. Full article

A naphthalimide-based fluorescent probe, Nap-I, with iodoacetamide as the alkylating group, has been synthesized, and its specific fluorescent staining of proteins containing cysteine (Cys) and selenocysteine (Sec) residues in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) has been evaluated. This molecule shows good fluorescence properties in the labeling of protein Cys/Sec residues, while reducing steric hindrance and minimizing changes in the water solubility of proteins. Reaction parameters, such as labeling time and pH, have been investigated, and the optimal labeling conditions for Cys-containing proteins have been determined. Thioredoxin reductase (TXNRD) is best stained at low pH. The probe Nap-I has been successfully used for the quantification of serum proteins and hemoglobin in Tan sheep serum, and TXNRD in Tan sheep liver and muscle has been labeled at low pH. Based on the probe Nap-I, we have also distinguished TXNRD1 and TXNRD2 by SDS-PAGE. The results showed that, compared with the normal microenvironment in which the protein resides, the lower the pH value, the greater the TXNRD activity. Full article

Regenerative medicine and stem cells could prove to be an effective solution to the problem of treating heart failure caused by ischemic heart disease. However, further studies on the understanding of the processes which occur during the regeneration of damaged tissue are needed. Microfluidic systems, which provide conditions similar to in vivo, could be useful tools for the development of new therapies using stem cells. We investigated how mesenchymal stem cells (MSCs) affect the metabolic activity of cardiac cells (rat cardiomyoblasts and human cardiomyocytes) incubated with a potent uncoupler of mitochondrial oxidative phosphorylation under microfluidic conditions. A cyanide p-trifluoromethoxyphenylhydrazone (FCCP) was used to mimic disfunctions of mitochondria of cardiac cells. The study was performed in a microfluidic system integrated with nanofiber mats made of poly-l-lactid acid (PLLA) or polyurethane (PU). The microsystem geometry allows four different cell cultures to be conducted under different conditions (which we called: normal, abnormal—as both a mono- and co-culture). Metabolic activity of the cells, based on the bioluminescence assay, was assessed in the culture’s performed in the microsystem. It was proved that stem cells increased metabolic activity of cardiac cells maintained with FCCP. Full article

In this work, a novel fluorescent probe with first-time-selected thiazepine backbone, TZPzine-1, was developed for selective detection of hydrazine in water samples and living cells. Chosen from our recent anti-cancer agents, TZPzine-1 inferred structurally based advantages of the optical adjustability and the hydrazine-trapping approach. It also showed applicable properties including high sensitivity (LOD = 50 nM), wide linear range (0–15 equiv.), high selectivity (especially from competing species), rapid response (within 20 min), and practical steadiness in various pH (6.0–11.0) and temperature (15–50 °C) conditions. To satisfy the interdisciplinary requirements in environmental toxicology, TZPzine-1 was successfully applied in water samples and living cells. We hope that the information in this work, as well as the concept of monitoring the nitrogen cycle, may be referable for future research on systematic management. Full article

Dengue is a major threat to public health globally. While point-of-care diagnosis of acute/recent dengue is available to reduce its mortality, a lack of rapid and accurate testing for the detection of previous dengue remains a hurdle in expanding dengue seroepidemiological surveys to inform its prevention, especially vaccination, to reduce dengue morbidity. This study evaluated ViroTrack Dengue Serostate, a biosensors-based semi-quantitative anti-dengue IgG (immunoglobulin G) immuno-magnetic agglutination assay for the diagnosis of previous and recent dengue in a single test. Blood samples were obtained from 484 healthy participants recruited randomly from two communities in Petaling district, Selangor, Malaysia. The reference tests were Panbio Dengue IgG indirect and capture enzyme-linked immunosorbent assays, in-house hemagglutination inhibition assay, and focus reduction neutralization test. Dengue Serostate had a sensitivity and specificity of 91.1% (95%CI 87.8–93.8) and 91.1% (95%CI 83.8–95.8) for the diagnosis of previous dengue, and 90.2% (95%CI 76.9–97.3) and 93.2% (95%CI 90.5–95.4) for the diagnosis of recent dengue, respectively. Its positive predictive value of 97.5% (95%CI 95.3–98.8) would prevent most dengue-naïve individuals from being vaccinated. ViroTrack Dengue Serostate’s good point-of-care diagnostic accuracy can ease the conduct of dengue serosurveys to inform dengue vaccination strategy and facilitate pre-vaccination screening to ensure safety. Full article

Paper-based analytical devices (PADs) and Electrospun Fiber-Based Biosensors (EFBs) have aroused the interest of the academy and industry due to their affordability, sensitivity, ease of use, robustness, being equipment-free, and deliverability to end-users. These features make them suitable to face the need for point-of-care (POC) diagnostics, monitoring, environmental, and quality food control applications. Our work introduces new and experienced researchers in the field to a practical guide for fibrous-based biosensors fabrication with insight into the chemical and physical interaction of fibrous materials with a wide variety of materials for functionalization and biofunctionalization purposes. This research also allows readers to compare classical and novel materials, fabrication techniques, immobilization methods, signal transduction, and readout. Moreover, the examined classical and alternative mathematical models provide a powerful tool for bioanalytical device designing for the multiple steps required in biosensing platforms. Finally, we aimed this research to comprise the current state of PADs and EFBs research and their future direction to offer the reader a full insight on this topic. Full article