In this study, a surface-enhanced Raman scattering (SERS) substrate based on high-refractive-index reflective glass beads (HRGBs) was prepared by a facile method and successfully applied to the detection of polycyclic aromatic hydrocarbons (PAHs). The HRGB-SERS substrate was prepared by depositing silver nanoparticles (Ag NPs) onto the surface of HRGBs. The preparation procedure of the substrate was simplified by accelerating the hydrolysis of (3-Aminopropyl) trimethoxysilane (APTMS) and increasing the concentration of Ag NPs. Compared with previous methods, the HRGB-SERS substrate prepared with one round of deposition has the same detection performance, a simpler preparation process, and lower cost. Additionally, halide ions were used to modify the substrate to increase the detection sensitivity of PAHs. Adding 10 mM KBr solution to the HRGB-SERS substrate was found to achieve the best modification effect. Under the optimal modification conditions, the detection sensitivity of pyrene was improved by 3 orders of magnitude (10⁻⁷ M). Due to the HRGB-SERS substrate’s excellent performance, the rapid identification and trace detection of spiked water samples mixed with anthracene, phenanthrene, and pyrene was realized using a Raman spectrometer with only a volume of 10 μL of the water samples. Full article

Photoactivated gallium nitride (GaN) nanowire-based gas sensors, functionalized with either bare In₂O₃ or In₂O₃ coated with a nanolayer of evaporated Au (Au/In₂O₃), were designed and fabricated for high-sensitivity sensing of NO₂ and low-power operation. The sensors were tested at room temperature under 265 nm and 365 nm ultraviolet illumination at several power levels and in relative humidity ranging from over 20% to 80%. Under all conditions, photoconductivity was lower in the Au/In₂O₃-functionalized sensors compared to that of sensors functionalized with bare In₂O₃. However, when tested in the presence of NO₂, the Au/In₂O₃ sensors consistently outperformed In₂O₃ sensors, the measured sensitivity being greater at 265 nm compared to 365 nm. The results show significant power reduction (×12) when photoactivating at (265 nm, 5 mW) compared to (365 nm, 60 mW). Maximum sensitivities of 27% and 42% were demonstrated with the Au/In₂O₃ sensors under illumination at (265 nm, 5 mW) for 1 ppm and 10 ppm concentration, respectively. Full article

Developing a simple and convenient approach for glucose sensing is crucially important in disease diagnosis and health monitoring. In this work, a glucose sensor based on plasmonic nanostructures was developed using gold–silver core–shell nanoparticles as the sensing platform. Based on the oxidative etching of the silver shell, the concentration of hydrogen peroxide and glucose could be determined quantitatively via the spectral change. This spectral change could also be observed with the naked eye or with a phone camera, realizing colorimetric sensing. To demonstrate this, glucose solutions at different concentrations were quantitatively detected in a wide concentration range of 0–1.0 mM using this colorimetric sensor. Importantly, shell thickness could significantly affect the sensitivity of our colorimetric sensor. This work provides a deeper understanding of the plasmonic sensing of glucose, which will help to realize its real applications. Based on this strategy, the non-invasive sensing of metabolites may be realized for disease diagnosis and health monitoring. Full article

There has been an increasing demand for rapid and sensitive techniques for the detection of heavy metal ions that are harmful to the human body in traditional Chinese medicine (TCM). However, the complex chemical composition of TCM makes the quantitative detection of heavy metal ions difficult. In this study, the magnetic Fe₃O₄@SiO₂@AuNPs nanoparticles combined with a probe molecule DMcT were used for the specific enrichment and detection of Hg²⁺ in the complex system of licorice. The core of Fe₃O₄ was bonded with SiO₂ to increase its stability. A layer of AuNPs was deposited to produce a “core–shell” Raman substrate with high surface-enhanced Raman spectroscopy (SERS) activity, which was surface modified by DMcT probe molecules with sulfhydryl groups. In the presence of Hg²⁺, Hg²⁺ binds to N on the amino group of DMcT to form N-Hg²⁺-N complexes, which induces Fe₃O₄@SiO₂@AuNPs-DMcT clustering to enhance SERS signal. The Raman probe molecule DMcT showed an excellent linear relationship (R² = 0.9709) between the SERS signal at 1416 cm⁻¹ and the Hg²⁺ concentration (0.5~100 ng/mL). This method achieved a good recovery (89.10~111.00%) for the practical application of detection of Hg²⁺ in licorice extracts. The results demonstrated that the functional Fe₃O₄@SiO₂@AuNPs-DMcT performed effective enrichment and showed high sensitivity and accurate detection of heavy metal ions from the analytes. Full article

Tungsten sulfide decorated with indium oxide nanoparticles (In₂O₃/WS₂) was studied for a chemiresistive-type NH₃ sensor at room temperature. It was found that the responses of the developed In₂O₃/WS₂ heterostructure nanocomposite-based sensors are significantly improved to 3.81 from 1.45 for WS₂. The response and recovery time of the heterostructure-based sensor was found to significantly decrease to 88 s/116 s (10 ppm) from 112 s/192 s for the WS₂-based one. The sensor also exhibits excellent selectivity and signal reproducibility. In comparison to WS₂ decorated with both ZnO and SnO₂ in similar ways, the In₂O₃-decorated WS₂ has overall better sensing performance in terms of sensitivity, selectivity and response/recovery speeds for NH₃ from 1 ppm to 10 ppm at room temperature. The improved sensing properties of WS₂ incorporating In₂O₃ could be attributed to the joint enhancement mechanisms of the “electronic and catalytic” sensitizations. Full article

In this paper, a composite of tin diselenide (SnSe₂) functionalized by graphite-phase carbon nitride (g-C₃N₄) was successfully prepared by a hydrothermal method, and was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). These microstructure characterization results verified the successful synthesis of a multilayer g-C₃N₄/rod-shaped SnSe₂ composite. The gas sensitivity results showed that when the g-C₃N₄ ratio was 30%, the g-C₃N₄/SnSe₂ composite sensor had the highest response (28.9%) at 200 °C to 20 ppm sulfur dioxide (SO₂) gas, which was much higher than those of pristine g-C₃N₄ and SnSe₂ sensors at the optimum temperature. A series of comparative experiments proved that the g-C₃N₄/SnSe₂ composite sensor demonstrated an excellent response, strong reversibility and good selectivity for ppm-level SO₂ gas detection. The possible SO₂ sensing mechanism was ascribed to the heterostructure between the n-type SnSe₂ and n-type g-C₃N₄ nanomaterials. Furthermore, we also proposed the influence of the special structure of the g-C₃N₄ functionalized SnSe₂ composite on the gas-sensing characteristics. Full article

A stable bimetallic catalyst composed of Co–Pd@Al₂O₃ was synthesized using a wet impregnation method, followed by calcination and H₂ reduction. The synthesized catalyst was thoroughly characterized using XRD, BET, SEM, EDX, and TPR techniques. The catalyst was then drop-casted on a glassy carbon electrode (Co–Pd@Al₂O₃/GCE) and applied for the sensitive and selective electrochemical determination of a common antidepressant drug, venlafaxine (VEN). The proposed sensor (Co–Pd@Al₂O₃/GCE) demonstrated a remarkable catalytic activity for the electro-oxidation of VEN, with a decent repeatability and reproducibility. The pH dependent responsiveness of the electro-oxidation of VEN helped in proposing the redox mechanism. A linear relationship between the peak current and concentration of VEN was observed in the range of 1.95 nM to 0.5 µM, with LOD and LOQ of 1.86 pM and 6.20 pM, respectively. The designed sensor demonstrated an adequate selectivity and significant stability. Moreover, the sensor was found to be quite promising for determining the VEN in biological specimens. Full article

Chemosensors based on traditional fluorescent dyes have always contributed to the development of chemical sensor areas. In this review, the rhodamine-based chemosensors’ improvements and applications from 2018 to 2022 are discussed, mainly focusing on cations (metal ions and H⁺), anions (CN⁻, F⁻, etc.), and small bio-functional molecules’ (thiols, amino acids, etc.) detection. Specifically, this review highlights the detection target, detection limit, detection solution system, detection mechanism, and performance of the rhodamine-based sensors. Although these rhodamine-based sensors are well developed, their repeatability and sensitivity still need significant improvement. This review is expected to bring new clues and bright ideas to researchers for further advances in rhodamine-based chemosensors in the future. Full article

In this review, we present the current trends in photonic biosensors, focusing on devices based on lab-on-a-chip (LOC) systems capable of simultaneously detecting multiple real-life diseases on a single platform. The first section lists the advantages and challenges of building LOC platforms based on integrated optics. Some of the most popular materials for the fabrication of microfluidic cells are also shown. Then, a review of the latest developments in biosensors using the evanescent wave detection principle is provided; this includes interferometric biosensors, ring resonators, and photonic crystals, including a brief description of commercial solutions, if available. Then, a review of the latest advances in surface plasmon resonance (SPR) biosensors is presented, including localized-SPRs (LSPRs). A brief comparison between the benefits and required improvements on each kind of biosensor is discussed at the end of each section. Finally, prospects in the field of LOC biosensors based on integrated optics are glimpsed. Full article

Plasmonics can bind light to their surface while increasing its intensity. The confinement and enhancement of light allows high–density, independent, subwavelength sensor elements to be constructed in micrometer–sized arrays. Plasmonic nanostructures have been widely used in the sensing field because of their fast, real–time and label–free characteristics. Numerous plasmonic metasensors have been configured for next–generation technologies since the emergence of metamaterials and metasurfaces. Among these applications, the development of high–sensitivity sensors based on new physical mechanisms has received tremendous interest recently. This review focuses on high–sensitivity plasmonic nanosensors and metasensors based on new physical mechanisms, especially based on Fano resonance and the exceptional point (EP). The asymmetric Fano resonance generated by the interference of different resonance modes has a narrower bandwidth, while an EP occurs whenever two resonant modes coalesce both in their resonant frequency and their rate of decay or growth. Both physical mechanisms could tremendously improve the sensitivity of the plasmonic sensors. We summarize the working principles, the latest development status and the development trends of these plasmonic nanosensors and metasensors. It is believed that these new sensing mechanisms can inspire more fruitful scientific research. Full article

Biochips are composed of arrays of micropatterns enabling the optical detection of target analytes. Inkjet printing, complementary to commercially available micro- and nanospotters, is a contactless and versatile micropatterning method. Surprisingly, the inkjet printing of molecularly imprinted polymers (MIPs), also known as biomimetic synthetic antibodies, has not been demonstrated as yet. In this work, core–shell structures are proposed through the combination of inkjet printing of the core (top-down approach) and controlled radical polymerization (CRP) to decorate the core with a thin film of MIP (bottom-up approach). The resulting biochips show quantitative, specific, and selective detection of antibiotic drug enrofloxacin by means of fluorescence analysis. Full article

Water contamination from endocrine disruptors has become a major problem for health issues. Estriol is a hormone often detected in several aquatic matrices, due to the inefficient removal of such compounds through conventional water treatment methods. Therefore, there is a continuous need to develop new, efficient, and low-cost treatment methods for this hormone removal, as well as analytical devices able to detect estriol at low concentrations. In this present study, we report the use of the Eichhornia crassipes (water hyacinth) as a phytoremediation agent for estriol removal from aqueous matrices, in addition to a newly developed electrochemical sensor based on reduced graphene oxide and copper nanoparticles as a quantification and monitoring tool of the hormone. The developed sensor presented a linear detection region from 0.5 to 3.0 μmol L⁻¹, with detection and quantification limits of 0.17 μmol L⁻¹ and 0.56 μmol L⁻¹, respectively. Phytoremediation experiments were conducted in 2 L beakers and the reducing levels of the hormone were studied. Water hyacinth was able to reduce contaminant levels by approximately 80.5% in 7 days and below detection limits in less than 9 days, which is a good alternative for water decontamination with this endocrine disruptor. Due to the hydrophobicity of estriol, the probable mechanism involved in the bioremediation process is rhizodegradation, and the decrease in pH in the beakers that contained the plants indicated a possible formation of biofilms on the roots. Full article

We investigated the easily synthesized ligand H₃L as a fluorescent chemosensor for the detection of CdSe nanoparticles (CdSe NPs) and L-cysteine-capped CdSe quantum dots (CdSe-Cys QDs) in ethanol–water samples. A drastic quenching of the fluorescence emission of H₃L at 510 nm occurred, as a result of the addition of CdSe NPs and CdSe-Cys QDs. A solution of H₃L (1.26 ppb) showed sensitive responses to both CdSe NPs and CdSe-Cys QDs, with limits of detection (LOD) as low as 40 and 62 ppb, respectively. Moreover, using a smartphone color recognizer application, the fluorescence intensity response of H₃L-modified cellulose paper to CdSe-Cys QDs was recorded on a red channel (R), which allowed us to detect CdSe-Cys QDs with LOD = 15 ppb. Interference of some common metal nanomaterials (NMs), as well as metal ions, in the determination of CdSe NMs in solution was studied. The affinity of H₃L to CdSe NPs and CdSe-Cys QDs was spectroscopically determined. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), micro-X-ray fluorescence (µ-XRF), ¹H-NMR, attenuated total reflection infrared spectroscopy (ATR-IR), and density functional theory (DFT) were also used to investigate the interaction of H₃L with CdSe NMs. Full article

In this work we present a dual optical and electrochemical sensor based on SiO₂/Si₃N₄ resonant nanopillars covered with an indium tin oxide (ITO) thin film. A 25–30 nm thick ITO layer deposited by magnetron sputtering acts as an electrode when incorporated onto the nanostructured array, without compromising the optical sensing capability of the nanopillars. Bulk sensing performances before and after ITO deposition have been measured and compared in accordance with theoretical calculations. The electrochemical activity has been determined by the ferri/ferrocyanide redox reaction, showing a remarkably higher activity than that of flat thin films of similar ITO nominal thickness, and proving that the nanopillar system covered by ITO presents electrical continuity. A label-free optical biological detection has been performed, where the presence of amyloid-β has been detected through an immunoassay enhanced with gold nanoparticles. Again, the experimental results have been corroborated by theoretical simulations. We have demonstrated that ITO can be a beneficial component for resonant nanopillars sensors by adding potential electrochemical sensing capabilities, without significantly altering their optical properties. We foresee that resonant nanopillars coated with a continuous ITO film could be used for simultaneous optical and electrochemical biosensing, improving the robustness of biomolecular identification. Full article

In this paper, the gas-sensitive properties of co-doping the rare earth element La and noble metal Au in In₂O₃ nanospheres were investigated for ethanol detection. Through XRD and SEM characterization, the grain size of La-In₂O₃ and Au/La-In₂O₃ nanoparticles was smaller than that of pure In₂O₃. As expected, the smaller grain size sample has shown a higher response for ethanol vapor. Compared with the pure In₂O₃ nanoparticles, the 2 mol%Au/2 mol%La-In₂O₃ sample has shown better ethanol-sensing properties, including higher sensitivity (S = 381) and lower operating temperature (210 °C) for 100 ppm ethanol vapor. In addition, the Au/La-In₂O₃ sensor presented a fast response time (1 s). The enhancement mechanism of the ethanol response was discussed for Au/La-In₂O₃ nanoparticles. The obtained experimental results would provide a new road for designing higher response sensors. Full article