Mercaptopyridine-Functionalized Gold Nanoparticles for Fiber-Optic Surface Plasmon Resonance Hg2+ Sensing

Detection of Hg2+ in environmental water conditions by using a reusable SERS-based microfluidic chip with a high specificity and sensitivity

This work reported a surface-enhanced Raman spectroscopy (SERS)-based microfluidic chip that detects mercury ions (Hg2+) in water with high sensitivity and good reproducibility. Silver nanoparticles (AgNPs) are easily fabricated on a Si substrate using a thin, thermally treated Ag film. Cy3 functionalized single-stranded DNA (Cy3-ssDNA) serves as the probe, which is immobilized on the AgNPs (Cy3-ssDNA/AgNPs), generating a SERS-based sensing surface. Due to the strong interaction between thymine (T) bases and Hg2+, in the presence of these ions, the ssDNA forms a T-Hg2+-T hairpin structure, which enhances the SERS signal. This method exhibits a limit of detection (LOD) of 1 × 10-13 M. Furthermore, the proposed SERS chip demonstrates exceptional selectivity for mercury ions, as well as good reusability. The reusability of the SERS microfluidic chip was evaluated using the L-cysteine, which has a stronger affinity than T for Hg2+. By applying L-cysteine, the chip can be reused 10 times for the detection of Hg2+ at concentrations as low as 1 × 10-8 M. The method proposed in this study shows good sensitivity and holds good potential for application in the detection of Hg2+.

Design of Core@Shell Nanoparticles Based on Gold and Magnetic NiFe Prussian-Blue Analogues Featuring Shape-Dependent Magnetic and Electrochemical Activity

Au@Prussian-Blue analogue (PBA) core@shell nanoparticles (NPs) are highly versatile nanostructures with complementary and shape-dependent properties of interest in the current technologies. However, due to the high reactivity of cyanides toward Au, scarce PBAs have been successfully synthesized in direct contact with Au NPs, leaving the formation of anisotropic Au@PBA NPs as a significant synthetic challenge. Here, we have developed a robust protocol for synthesizing core@shell NPs, composed of a magnetic CsNi[Fe(CN)6] PBA shell grown on individual Au NPs, regardless of the core morphology (spheres, rods, or stars). Specifically, the uniqueness of our protocol lies in the prior Au core functionalization with anchoring molecules that facilitate PBA growth while preventing Au etching and preserving the initial oxidation states of the metals. This has afforded direct growth of ferromagnetic NiIIFeIII PBAs on Au NPs. Moreover, by exploiting the structural mismatch at the Au/PBA interface and the curvature of anisotropic Au templates, we manage to induce a substantial structural strain within the PBA shell. When star-shaped Au nanoparticles are used, a maximum strain of 2.0% is reached. This strain combined with an increased polycrystallinity lead to modifications in the PBA catalytic properties, resulting in a 10-fold improvement in the intrinsic electrocatalytic activity.

Carbon Quantum Dots Based Nanocomposite for Selective Mercury Detection

The emergence of 2D carbon-based materials has a profound impact on various research areas, such as biosciences, electronics, optics, environmental protection, and monitoring. Mercury, a highly toxic pollutant, can cause severe health complications such as neural toxicity, insomnia, cognitive dysfunction, muscle atrophy, peripheral vision impairment, and emotional instability. A suitable 2D nanostructural interface is required to effectively monitor mercury levels in the environment. This study presents the use of synergistic nitrogen and sulfur co-doped carbon quantum dots anchored on exfoliated molybdenum disulfide for rapid detection of mercury ions. This process employs a biomass extract that facilitates the exfoliation of bulk molybdenum disulfide and also act as carbon precursor for in situ carbon quantum dot deposition on exfoliated molybdenum disulfide. The nanocomposite provides photo-physical properties and surface functionalities from both organic and inorganic components to bridge the charge transfer, resulting from selective binding of mercury (II) ions. This 2D heterojunction is capable of detecting mercury (II) ions with a response time of ≈90 s, limit of detection of 31pm, and photosensitivity of 16.6A cm-2 M-1. The interface is tested on blood samples from Labeorohita fish to detect mercury (II) toxicity in nature.

Synthesis of 2MP-CuNPs Fluorescent Probes and Their Application in Tetracycline Detection

A fluorescent probe composed of 2-mercaptopyridine-copper nanoparticles (2MP-CuNPs) was synthesized through a hydrothermal method utilizing CuCl2 and 2-mercaptopyridine (2MP). The experimental results indicate that the 2MP-CuNPs probe exhibited an excellent fluorescence emission peak at 525 nm with an excitation wavelength of 200 nm. Furthermore, this emission peak was accompanied by a substantial Stokes shift of 325 nm, which effectively minimized the overlap between the excitation and emission spectra, thereby enhancing detection sensitivity. In tetracycline (TC) detection, the dimethylamino group on TC undergoes protonation in acidic conditions, resulting in a H+ ion. Consequently, the nitrogen atom within the pyridine moiety of the 2MP-CuNPs probe forms a coordination complex with H+ via multi-toothed n-bonding interactions, leading to a significant reduction in fluorescence intensity at 525 nm. Based on this mechanism, a quantitative detection method for TC was successfully established with a linear range spanning from 0.1 to 240 µM and an impressive detection limit of 120 nM. Furthermore, during actual sample analyses involving milk and chicken feed, this analysis method based on the 2MP-CuNPs probe achieved absolute recovery rates ranging from 94% to 98%, underscoring its considerable potential for practical applications.

A Review on Pyridine Based Colorimetric and Fluorometric Chemosensor for Detection of Hg2+ ion

Pyridine, N-containing heterocyclic organic compound, displays strong coordination capabilities with various metal ions. It can be synthesized through various methods, such as Friedlander synthesis, heterocumulene synthesis, cross-coupling reactions, the Radziszewski reaction, Bonnemann cyclization, as well as cobalt-catalyzed synthesis. Experimental and spectroscopic analyses have demonstrated a strong binding affinity between pyridine and several heavy metal ions, including Pb2+, Hg2+, and Cd2+ ions. The escalating environmental pollution caused by the disposal of heavy metal ions in rivers, open air, and water reservoirs poses a significant threat to both ecosystem and human health. To address these environmental challenges, a cost-effective and easily synthesized chemosensor has been prepared for identifying toxic heavy metal ions in various samples. Pyridine's photophysical properties make it an effective sensor for detecting Hg2+ ions, displaying fluorescence quenching or enhancement in their presence. The coordination between pyridine and Hg2+ ions lead to shifts in the absorption spectra. The pyridine-based sensor has been evaluated for its sensitivity, selectivity, and detection limits under different experimental conditions. Pyridine's solubility and environmental stability make it applicable for real-time detection, making pyridine probes valuable tool for monitoring toxic Hg2+ ions in the environment. The results demonstrate that the pyridine-based chemosensor exhibits good selectivity and sensitivity for targeting Hg2+ ions, with detection limits within acceptable ranges. This review (from years 2011 to 2023) emphasizes the preparation of various substituted pyridine compounds as selective, sensitive, and specific sensors for real-time detection of Hg2+ ions.

Applications of Novel Microscale and Nanoscale Materials for Theranostics: From Design to Clinical Translation

The growing global prevalence of chronic diseases has highlighted the limitations of conventional drug delivery methods, which often suffer from non-specific distribution, systemic toxicity, and poor bioavailability. Microscale and nanoscale materials have emerged as innovative solutions, offering enhanced targeting, controlled release, and the convergence of therapeutic and diagnostic functions, referred to as theranostics. This review explores the design principles, mechanisms of action, and clinical applications of various novel micro- and nanomaterials in diseases such as cancer, cardiovascular disorders, and infectious diseases. These materials enable real-time monitoring of therapeutic responses and facilitate precision medicine approaches. Additionally, this paper addresses the significant challenges hindering clinical translation, including biocompatibility, potential toxicity, and regulatory issues. Ongoing clinical trials demonstrate the potential of nanomaterials in theranostic applications, but further research is needed to overcome the barriers to widespread clinical adoption. This work aims to contribute to the acceleration of integrating nanomedicine into clinical practice, ultimately enhancing the efficacy and safety of therapeutic interventions.

Gold Nanocluster: A Photoelectric Converter for X-Ray-Activated Chemotherapy

Despite the promise of activatable chemotherapy, the development of a spatiotemporally controllable strategy for prodrug activation in deep tissues remains challenging. Herein, a proof-of-concept is proposed for a gold nanocluster-based strategy that utilizes X-ray irradiation to trigger the liberation of platinum (Pt)-based prodrug conjugates, thus enabling radiotherapy-directed chemotherapy. Mechanistically, the irradiated activation of prodrugs is achieved through direct photoelectron transfer from the excited-state gold nanoclusters to the Pt(IV) center, resulting in the release of cytotoxic Pt(II) agents. Compared to the traditional combination of chemotherapy and radiotherapy, this radiotherapy-directed chemotherapy strategy offers superior antitumor efficacy and safety benefits through spatiotemporal synergy at the tumor site. Additionally, this strategy elicits robust immunogenic cell death and yields profound outcomes for combined immunotherapy of breast cancer. This versatile strategy is ushering in a new era of radiation-mediated chemistry for controlled drug delivery and the precise regulation of biological processes.

Advancements in mercury detection using surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs): a review

Mercury (Hg) contamination remains a major environmental concern primarily due to its presence at trace levels, making monitoring the concentration of Hg challenging. Sensitivity and selectivity are significant challenges in the development of mercury sensors. Surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs) are two distinct analytical methods developed and employed for mercury detection. In this review, we provide an overview of the key aspects of SERS and IIP methodologies, focusing on the recent advances in sensitivity and selectivity for mercury detection. By examining the critical parameters and challenges commonly encountered in this area of research, as reported in the literature, we present a set of recommendations. These recommendations cover solid and colloidal SERS substrates, appropriate Raman reporter/probe molecules, and customization of IIPs for mercury sensing and removal. Furthermore, we provide a perspective on the potential integration of SERS with IIPs to achieve enhanced sensitivity and selectivity in mercury detection. Our aim is to foster the establishment of a SERS-IIP hybrid method as a robust analytical tool for mercury detection across diverse fields.

Loading of AuNCs with AIE effect onto cerium-based MOFs to boost fluorescence for sensitive detection of Hg2. Talanta 2024;273:125843. [PMID: 38492285 DOI: 10.1016/j.talanta.2024.125843] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Ligand-protected gold nanoclusters (AuNCs) have become promising nanomaterials in fluorescence (FL) methods for mercury ions (Hg2+) monitoring, but low FL efficiency hinders their widespread application. Herein, AuNCs/cerium-based metal-organic frameworks (AuNCs/Ce-MOFs) were prepared by loading 6-aza-2-thiothymine-protected AuNCs (ATT-AuNCs) with aggregation-induced emission (AIE) effect on the surface of Ce-MOFs by electrostatic attraction. This strategy improved the FL intensity of AuNCs through two aspects: (i) the AIE effect of ATT-AuNCs and (ii) the confinement effect of Ce-MOFs, which improved the restriction of intramolecular motion (RIM) of ATT-AuNCs. In addition, Ce-MOFs could adsorb and aggregate Hg2+ during detection, which might increase the local concentration. Therefore, based on the high FL signal of AuNCs/Ce-MOFs and enriched Hg2+, sensitive detection of Hg2+ could be achieved. More importantly, the strong specific recognition between AuNCs and Hg2+ could guarantee selectivity. The developed FL sensor exhibited superior detection performances with a wide linear range of 0.2-500 ng mL-1 and a low detection limit of 0.067 ng mL-1. Furthermore, the FL sensor used for sensitive and selective detection of Hg2+ in real samples, and the results agreed well with the standard method. In summary, this work proposed an effective and generalized strategy for improving the FL efficiency of AuNCs, which would greatly facilitate their application in pollutant monitoring.

Efficient 2D MOFs nanozyme combining with magnetic SERS substrate for ultrasensitive detection of Hg2

Biomimetic inorganic nanoenzyme is a kind of nanomaterial with long-term stability, easy preparation and low cost, which could instead of natural biological enzyme. Metal-organic framework (MOFs) as effectively nanoenzyme was attracted more attention for the adjustability and large specific surface area. This design is based on the catalase-like catalytic activity of 2D metal-organic frameworks (MOFs) and the high sensitivity of surface enhanced Raman spectroscopy (SERS) biosensors to construct a novel SERS biosensor capable of efficiently detecting mercury (Hg2+). In this study, 2D MOFs nanozyme was instead of 3D structure with more effecient catalytic site, which can catalyze o-Phenylenediamine (OPD) to OPDox with the assistance of H2O2. Besides, a magnetic composite nanomaterial Fe3O4@Ag@OPD was prepared as a signal carrier. In the presence of Hg2+, T-Hg2+-T base pairs were used to connect the two materials to realize Raman signal change. Based on this principle, the SERS sensor can realize the sensitive detection of Hg2+, the detection range is 1.0 × 10-12 ∼ 1.0 × 10-2 mol‧L-1, and the detection limit is 1.36 × 10-13 mol‧L-1. This method greatly improves the reliability of SERS sensor for detecting the target, and provides a new idea for detecting metal ions in the environment.

FO-SPR Model for Full-Spectrum Signal Analysis of Back-reflecting FO-SPR Sensors to Monitor MOF Deposition

In this study, we explore the full-spectrum capabilities of fiber-optic surface plasmon resonance (FO-SPR) for analyzing heterogeneous samples with increased comprehensiveness. Our approach involves refining a literature-derived FO-SPR model to more precisely reflect experimental data obtained using a back-reflecting sensor configuration. Key enhancements in our model include adjustments to the thickness and permittivity of the gold SPR-active layer on the FO-SPR sensor as well as improvements to the angular distribution of light within the system. We apply this optimized model to the investigation of the deposition process of a metal-organic framework (MOF), specifically ZIF-8, using FO-SPR. By closely examining the temporal variations in the FO-SPR signal during MOF layer formation, we simultaneously determine the evolving thickness and refractive index (RI) of the MOF layer, offering a dual-parameter analysis. Our results demonstrate that a full-spectrum analysis of the FO-SPR signal can extract critical information from samples exhibiting radial heterogeneity. This advancement significantly enhances the quantitative assessment of various phenomena that alter the refractive index in the sensor's domain, such as adsorption and binding processes. This work thus represents a significant step forward in the field of FO-SPR sensor technology, promising broad applications in areas requiring the precise detection and analysis of complex samples.

An in-fiber sensor for simultaneous measurement of cholesterol concentration and temperature based on SPR and MMI

In this paper, we design an in-fiber two-parameter sensor with multimode fiber (MMF)-Au film coated hollow fiber (HCF)-MMF structure, which can simultaneously excite Surface Plasmon Resonance (SPR) effect and Multimode Interference (MMI) effect. A composite material of Au nanoparticles/β-cyclodextrin (AuNPs/β-CD) is deposited on the surface of the Au film coated HCF to realize highly-sensitive measurement of cholesterol concentration. Here, the AuNPs can not only enhance the measurement sensitivity of the SPR sensor, but also increase the numbers of combination sites of β-CD and cholesterol. Then, to solve the cross-sensitivity problem between temperature and cholesterol, the glycerin is selected as a temperature-sensitive material to fill into the inner channel of the HCF, making the MMI sensor sensitive to temperature, and finally realizing the simultaneous measurement of cholesterol concentration and temperature. The experimental results demonstrate that the wavelength shift of the SPR and the MMI are 12.7 nm and 7.9 nm, respectively, when the cholesterol concentration changes from 0 to 500 nM. The temperature sensitivity of the SPR and the MMI are -0.9 nm/°C and 2.64 nm/°C, respectively, in the temperature range of 30°C-46 °C. In addition, the sensor shows good recognition ability of cholesterol molecules in serum environment, with good stability, selectivity and repeatability, and has broad application prospects in the biomedical field.

Lab-on-Fiber Sensors with Ag/Au Nanocap Arrays Based on the Two Deposits of Polystyrene Nanospheres

Surface-enhanced Raman spectroscopy (SERS) can boost the pristine Raman signal significantly which could be exploited for producing innovative sensing devices with advanced properties. However, the inherent complexity of SERS systems restricts their further applications in rapid detection, especially in situ detection in narrow areas. Here, we construct an efficient and flexible SERS-based Lab-on-Fiber (LOF) sensor by integrating Ag/Au nanocap arrays obtained by Ag/Au coating polystyrene nanospheres on the optical fiber face. We obtain rich "hot spots" at the nanogaps between neighboring nanocaps, and further achieve SERS performance with the assistance of laser-induced thermophoresis on the metal film that can achieve efficiency aggregation of detected molecules. We achieve a high Raman enhancement with a low detection limitation of 10-7 mol/L for the most efficient samples based on the above sensor. This sensor also exhibits good repeatability and stability under multiple detections, revealing the potential application for in situ detection based on the reflexivity of the optical fiber.

Magnetic MOF Substrates for the Rapid and Sensitive Surface-Enhanced Raman Scattering Detection of Uranyl

With the widespread use of uranium in the nuclear industry, achieving rapid and sensitive detection of uranium contaminants is critical for reducing environmental pollution. Surface-enhanced Raman scattering (SERS), with its high sensitivity and unique fingerprint properties, has been used for the analysis of uranyl. However, the weak affinity of Au for uranyl remains a challenge in the development of spherical Au-based SERS substrates. The metal-organic framework (MOF) material ZIF-8 exhibits excellent adsorption capacity for uranyl and could overcome this limitation. In this study, ZIF-8 porous structures were modified on a magnetic SERS substrate, Fe3O4@SiO2@Au (FA), for the rapid and sensitive detection and analysis of the uranyl species. Uranyl was adsorbed by ZIF-8, allowing ready access to the hot spots in the interstices of Au nanoparticles (AuNPs). Symmetrically stretched vibrating bonds of O═U═O were detected at 829 cm-1 as the characteristic peak of uranyl by surface plasmon resonance between the AuNPs. The ZIF-8 coating had minimal influence on target detection as the detection limit for 4-MPY was only half an order of magnitude lower than before modification. The enhancement factor for uranyl reached 106. The substrate showed excellent sensing performance in a neutral or alkaline environment. It was used to detect uranyl in tap water and river water; rapid separation of the species from the water samples was achieved using an external magnet to extract radioactive waste. The proposed substrate offers a route for monitoring and detecting uranyl contamination and an approach for achieving rapid on-site detection, providing a promising application for environmental contaminant detection.

One-step and real-time detection of Hg2+ in brown rice flour using a biosensor integrated with AC electrothermal enrichment

Mercury (Hg²⁺) is one of the most toxic heavy metals in farm products, so rapid detection of trace Hg²⁺ has always been sought after with high interest. Herein, we report a biosensor to specifically recognize Hg²⁺ in leaching solutions of brown rice flour. This sensor is simple and of low cost, with a very short assay time of 30 s. Another merit is the ultra-low limit of detection (LOD) at fM level. In addition, the specific aptamer probe realizes a good selectivity above 10⁵: 1 against the interferences. This sensor is developed based on an aptamer-modified gold electrode array (GEA) for capacitive sensing. Alternating current electrothermal (ACET) enrichment is induced during the AC capacitance acquirement. Thus, the enrichment and detection are coupled as a single step, and pre-concentration is needless. Owing to the sensing mechanism of solid-liquid interfacial capacitance and ACET enrichment, Hg²⁺ level can be sensitively and rapidly reflected. Also, the sensor has a wide linear range from 1 fM to 0.1 nM and a shelf life of 15 days. This biosensor shows advantages on overall performance, enabling easy-to-operate, real-time, and large-scale Hg²⁺ detection in farm products.

Adhesive surface-enhanced Raman scattering Cu-Au nanoassembly for the sensitive analysis of particulate matter

Surface-enhanced Raman scattering (SERS) has been used in atmospheric aerosol detection as it enables the high-resolution analysis of particulate matter. However, its use in the detection of historical samples without damaging the sampling membrane while achieving effective transfer and the high-sensitivity analysis of particulate matter from sample films remains challenging. In this study, a new type of SERS tape was developed, consisting of Au nanoparticles (NPs) on an adhesive double-sided Cu film (DCu). The enhanced electromagnetic field generated by the coupled resonance of the local surface plasmon resonances of AuNPs and DCu led to an enhanced SERS signal with an experimental enhancement factor of 10⁷. The AuNPs were semi-embedded and distributed on the substrate, and the viscous DCu layer was exposed, enabling particle transfer. The substrates exhibited good uniformity and favorable reproducibility with relative standard deviations of 13.53% and 9.74% respectively, and the substrates could be stored for 180 days with no signs of signal weakening. The application of the substrates was demonstrated by the extraction and detection of malachite green and ammonium salt particulate matter. The results demonstrated that SERS substrates based on AuNPs and DCu are highly promising in real-world environmental particle monitoring and detection.

Advances in Portable Heavy Metal Ion Sensors

Heavy metal ions, one of the major pollutants in the environment, exhibit non-degradable and bio-chain accumulation characteristics, seriously damage the environment, and threaten human health. Traditional heavy metal ion detection methods often require complex and expensive instruments, professional operation, tedious sample preparation, high requirements for laboratory conditions, and operator professionalism, and they cannot be widely used in the field for real-time and rapid detection. Therefore, developing portable, highly sensitive, selective, and economical sensors is necessary for the detection of toxic metal ions in the field. This paper presents portable sensing based on optical and electrochemical methods for the in situ detection of trace heavy metal ions. Progress in research on portable sensor devices based on fluorescence, colorimetric, portable surface Raman enhancement, plasmon resonance, and various electrical parameter analysis principles is highlighted, and the characteristics of the detection limits, linear detection ranges, and stability of the various sensing methods are analyzed. Accordingly, this review provides a reference for the design of portable heavy metal ion sensing.

Integrated Signal Amplification on a Fiber Optic SPR Sensor Using Duplexed Aptamers

Throughout the past decades, fiber optic surface plasmon resonance (FO-SPR)-based biosensors have proven to be powerful tools for both the characterization of biomolecular interactions and target detection. However, as FO-SPR signals are generally related to the mass that binds to the sensor surface, multistep processes and external reagents are often required to obtain significant signals for low molecular weight targets. This increases the time, cost, and complexity of the respective bioassays and hinders continuous measurements. To overcome these requirements, in this work, cis-duplexed aptamers (DAs) were implemented on FO-SPR sensors, which underwent a conformational change upon target binding. This induced a spatial redistribution of gold nanoparticles (AuNPs) upon specific target binding and resulted in an amplified and concentration-dependent signal. Importantly, the AuNPs were covalently conjugated to the sensor, so the principle does not rely on multistep processes or external reagents. To implement this concept, first, the thickness of the gold fiber coating was adapted to match the resonance conditions of the surface plasmons present on the FO-SPR sensors with those on the AuNPs. As a result, the signal obtained due to the spatial redistribution of the AuNPs was amplified by a factor of 3 compared to the most commonly used thickness. Subsequently, the cis-DAs were successfully implemented on the FO-SPR sensors, and it was demonstrated that the DA-based FO-SPR sensors could specifically and quantitatively detect an ssDNA target with a detection limit of 230 nM. Furthermore, the redistribution of the AuNPs was proven to be reversible, which is an important prerequisite for continuous measurements. Altogether, the established DA-based FO-SPR bioassay holds much promise for the detection of low molecular weight targets in the future and opens up possibilities for FO-SPR-based continuous biosensing.

Chromophoric Ion Receptor-Decorated Porous Monolithic Polymer for the Solid-State Naked Eye Sensing of Hg(II): An Experimental and Theoretical Approach

The current work presents a perspective to obliterate toxic Hg(II) from an aqueous environment, a strategic environmental remediation and decontamination measure. We report a simple, efficient, and reusable solid-state visual sensing strategy for the selective detection and quantitative recovery of ultratrace Hg(II). The capture of Hg(II) ions was effectuated using a macro-/mesoporous polymer monolith uniformly decorated with an azo-based chromophoric ion receptor, i.e., 7-((1H-benzo[d]imidazol-2-yl)diazenyl)quinolin-8-ol (BIDQ). The porous polymer template was synthesized through free radical polymerization of gylcidylmethacrylate and ethylene glycol dimethacrylate, leading to distinct structural and surface properties that offer exclusive solid-state colorimetric selectivity for Hg(II) upon restricted spatial dispersion of the ion receptor. The sensor provides a broad linear response range of 1-200 μg/L, with an outstanding detection limit of 0.2 μg/L for Hg(II) ions, thus effectuating reliable and reproducible sensing. Optimizing analytical parameters such as solution pH, receptor concentration, sensor quantity, kinetics, temperature, and matrix interference proved to be promising for the real-time monitoring of toxic mercury ions from aqueous/industrial systems, with maximum response in the pH range of 7.5-8.0, with a response time of ≤80 s. Density functional theory (DFT) calculations were employed to study the electronic structure of BIDQ upon chelating with Hg(II) ions, using 6-311G and LAND2Z basis sets.

Hybrid modes in gold nanoslit arrays on Bragg nanostructures and their application for sensitive biosensors

In this work, we present high-performance surface plasmonic sensors using gold nanostructures and Bragg photonic structures. The gold film on the Bragg structure provides Tamm plasmon states (TPs). The Fano coupling between higher order TPs and Bloch-wave surface plasmon polariton (BW-SPP) on the gold nanoslit array results in a new hybrid Tamm-plasmon mode. Using finite-difference time-domain calculations, we demonstrate that the hybrid mode has the advantages of high surface sensitivity of BW-SPP mode and high resonant quality of Tamm state. The calculated plasmonic field distribution shows that the hybrid mode has a similar evanescent distribution with BW-SPP mode on gold surface and TPs field in the Bragg structure. The experimental results verify that the hybrid mode has one hundred times higher wavelength sensitivity than the Tamm state. The figure of merit of the hybrid mode is five times better than the BW-SPP mode in conventional nanoslit arrays. The real-time sensorgram further confirms that the hybrid mode has a much higher sensitivity and better signal to noise ratios in the biomolecular interaction measurement.

Plasmonic fiber-optic sensing system for in situ monitoring the capacitance and temperature of supercapacitors

Compared with ex situ measurement, the in situ measurement is more suitable for inspecting complex electrochemical reactions and improving the intelligent energy storage management. However, most of the in situ investigation instruments are bulky and expensive. Here we demonstrate a miniaturized, portable, and low-cost fiber-optic sensing system for in situ monitoring the capacitance and temperature. It can help evaluate the self-discharge rate in supercapacitors (SCs). The fiber-optic sensing system with two probes are implanted inside the SCs to monitor the capacitance and temperature, respectively. The dual fiber-optic probes can work independently and avoid cross-interference through structure design. The fiber-optic localized surface plasmon resonance (LSPR) probe near the electrode surface can detect the capacitance in real-time by monitoring ion aggregation on the opposite electrode. The fiber-optic surface plasmon resonance (SPR) probe encapsulated in the thermosensitive liquid can independently detect the temperature change. The measurement uncertainties of the two sensing probes are 5.6 mF and 0.08 ℃, respectively. The proposed tiny and flexible fiber-optic sensing system provides a promising method for in situ monitoring the critical parameters. It is also a powerful tool for investigating electrochemical reactions in various energy storage devices.

Detection and imaging of Hg(II) in vivo using glutathione-functionalized gold nanoparticles

The optical and biological properties of functionalized gold nanoparticles (GNPs) have been widely used in sensing applications. GNPs have a strong binding ability to thiol groups. Furthermore, thiols are used to bind functional molecules, which can then be used, for example, to detect metal ions in solution. Herein, we describe 13 nm GNPs functionalized by glutathione (GSH) and conjugated with a rhodamine 6G derivative (Rh6G2), which can be used to detect Hg(II) in cells. The detection of Hg²⁺ ions is based on an ion-catalyzed hydrolysis of the spirolactam ring of Rh6G2, leading to a significant change in the fluorescence of GNPs-GSH-Rh6G2 from an "OFF" to an "ON" state. This strategy is an effective tool to detect Hg²⁺ ions. In cytotoxicity experiments, GNPs-GSH-Rh6G2 could penetrate living cells and detect mercury ions through the fluorescent "ON" form.

Surfactant stabilized gold nanomaterials for environmental sensing applications - A review

Surfactant stabilized Gold (Au) nanomaterials (NMs) have been documented extensively in recent years for numerous sensing applications in the academic literature. Despite the crucial role these surfactants play in the sensing applications, the comprehensive reviews that highlights the fundamentals associated with these assemblies and impact of these surfactants on the properties and sensing mechanisms are still quite scare. This review is an attempt in organizing the vast literature associated with this domain by providing critical insights into the fundamentals, preparation methodologies and sensing mechanisms of these surfactant stabilized Au NMs. For the simplification, the surfactants are divided into the typical and advanced surfactants and the Au NMs are classified into Au nanoparticles (NPs) and Au nanoclusters (NCs) depending upon the complexity in structure and size of the NMs respectively. The preparative methodologies are also elaborated for enhancing the understanding of the readers regarding such assemblies. The case studies regarding surfactant stabilized Au NMs were further divided into colorimetric sensors, surface plasmonic resonance (SPR) based sensors, luminescence-based sensors, and electrochemical/electrical sensors depending upon the property utilized by the sensor for the sensing of an analyte. Future perspectives are also discussed in detail for the researchers looking for further progress in that particular research domain.

Contamination, exposure, and health risk assessment of Hg in Pakistan: A review

Mercury is a highly toxic and highly mobile heavy metal. It has been regarded as more toxic than other nonessential and toxic nonradioactive heavy metals. Moreover, it has a high tendency of bioaccumulation and biomagnification in the ecosystem. This study aimed to assess the environmental and health risks related to Hg. Seventy studies related to Hg in environmental media, aquatic biota, and food stuffs across Pakistan were reviewed, and their concentrations were used for ecological and human health risk assessments. High concentrations of Hg were reported in the environment, with maximum concentrations of 72 mg L^-1, 144 mg kg^-1, 887 mg kg^-1, and 49,807 ng m^-3 in surface water, surface soil, surface sediments, and urban atmosphere, respectively. The possible non-carcinogenic health risk (hazard quotient) of Hg was assessed in soil, water, and fish. High risks were calculated for seafood and vegetable consumption, while low risks were estimated for soils and groundwater ingestion and exposure. Overall, children showed higher risks than adults. Last, the risk quotient analysis (RQ) revealed significant risks for aquatic species. RQs showed that multiple species, especially those with smaller resilience, could face long-term detrimental impacts. High, medium, and low risks were calculated from 66.66, 16.17, and 16.17% of the reported Hg concentrations.

Chemical-Based Surface Plasmon Resonance Imaging of Fingerprints

Fingerprints are extremely useful in personal identification; however, they are usually based on physical rather than chemical images because it remains a challenge to reveal a clear chemical fingerprint easily and sensitively. Herein, a surface plasmon resonance imaging (SPRi) method, combined with a chemically selective stepwise signal amplification (CS³A) strategy, is proposed to chemically image fingerprints with adjustable sensitivity and clarity. High-fidelity glucose-associated fingerprint images were obtained at five to seven cycles of CS³A based on the recognition reaction of concanavalin A (ConA) with dextran. The method is also extendable to image substances that possess and/or can be tagged with ConA- or dextran-recognizable groups. For demonstration, SPRi of carboxylic substances was conducted by amidating the carboxyl group with glucosamine to enable the ConA-based CS³A. Glucose- and carboxyl-based fingerprints were simultaneously and clearly imaged, allowing us to perform quantitative analysis of the representative of either glucose or amino acid (e.g., serine) or both. The curves measured from the standard spots were linear in the ranges of 1-4000 μM for glucose and 3.2-4000 μM for serine, with linear correlated coefficients of 0.9979 and 0.9962, respectively. It was then applied to the study of metabolic secretions in fingerprints during running exercise, yielding variation tendencies similar to those measured from sweat samples in the literature. As a noninvasive tool, the CS³A-coupled SPRi reveals both clear images of fingerprints and quantitative chemical information, and it is anticipated to become a competitive new method for chemically imaging fingerprints.

Gold Nanoparticles Based Optical Biosensors for Cancer Biomarker Proteins: A Review of the Current Practices

Cancer prognosis depends on the early detection of the disease. Gold nanoparticles (AuNPs) have attracted much importance in biomedical research due to their distinctive optical properties. The AuNPs are easy to fabricate, biocompatible, surface controlled, stable, and have surface plasmonic properties. The AuNPs based optical biosensors can intensely improve the sensitivity, specificity, resolution, penetration depth, contrast, and speed of these devices. The key optical features of the AuNPs based biosensors include localized surface plasmon resonance (LSPR), SERS, and luminescence. AuNPs based biomarkers have the potential to sense the protein biomarkers at a low detection level. In this review, the fabrication techniques of the AuNPs have been reviewed. The optical biosensors based on LSPR, SERS, and luminescence are also evaluated. The application of these biosensors for cancer protein detection is discussed. Distinct examples of cancer research that have a substantial impact on both scientific and clinical research are presented.

Metal-Nanostructure-Decorated Spider Silk for Highly Sensitive Refractive Index Sensing

Highly sensitive detection of refractive index (RI) is essential for the analysis of the bio-microenvironment and basic cellular reactions. To achieve this, optic-fiber RI sensors based on localized surface plasmon resonance (LSPR) have been widely used for their flexibility and high sensitivity. However, the current optic-fiber RI sensors are mainly fabricated using glass, which makes them face the challenges in biocompatibility and biosafety. In this work, a RI sensor with high sensitivity is fabricated using metal-nanostructure-decorated spider silk. The spider silk, which is directly dragged from Araneus ventricosus, is natural protein-based biopolymer with low attenuation, good biocompatibility and biodegradability, large RI, great flexibility, and easy functionalization. Hence, the spider silk can be an ideal alternative to glass for sensing in biological environments with a wide RI range. Different kinds of metal nanostructures, such as gold nanorods (GNRs), gold nanobipyramids (GNBP), and Ag@GNRs, are decorated on the surface of the spider silk utilizing the surface viscidity of the silk. By directing a beam of white light into the spider silk, the LSPR of the metal nanostructures was excited and a highly sensitive RI sensing (the highest sensitivity of 1746 nm per refractive index was achieved on the GNBP-decorated spider silk) was obtained. This work may pave a new way to precise and sensitive biosensing and bioanalysis.

Enzyme Sensing Using 2-Mercaptopyridine-Carbonitrile Reporters and Surface-Enhanced Raman Scattering

The high sensitivity and functional group selectivity of surface-enhanced Raman scattering (SERS) make it an attractive method for enzyme sensing, but there is currently a severe lack of enzyme substrates that release SERS reporter molecules with favorable detection properties. We find that 2-mercaptopyridine-3-carbonitrile ( o-MPN) and 2-mercaptopyridine-5-carbonitrile ( p-MPN) are highly effective as SERS reporter molecules that can be captured by silver or gold nanoparticles to give intense SERS spectra, each with a distinctive nitrile peak at 2230 cm-1. p-MPN is a more sensitive reporter and can be detected at low nanomolar concentrations. An assay validation study synthesized two novel substrate molecules, Glc-o-MPN and Glc-p-MPN, and showed that they can be cleaved efficiently by β-glucosidase (K m = 228 and 162 μM, respectively), an enzyme with broad industrial and biomedical utility. Moreover, SERS detection of the released reporters ( o-MPN or p-MPN) enabled sensing of β-glucosidase activity and β-glucosidase inhibition. Comparative experiments using a crude almond flour extract showed that the presence of β-glucosidase activity could be confirmed by SERS detection in a much shorter time period (>10 time shorter) than by UV-vis absorption detection. It is likely that a wide range of enzyme assays and diagnostic tests can be developed using 2-mercaptopyridine-carbonitriles as SERS reporter molecules.

A Versatile One-Step Competitive Fiber Optic Surface Plasmon Resonance Bioassay Enabled by DNA Nanotechnology

Fiber optic surface plasmon resonance (FO-SPR)-based biosensors have emerged as powerful tools for biomarker detection due to their ability for real-time analysis of biomolecular interactions, cost-effectiveness, and user-friendliness. However, as (FO-)SPR signals are determined by the mass of the target molecules, the detection of low-molecular-weight targets remains challenging and currently requires tedious labeling and preparation steps. Therefore, in this work, we established a new concept for low-molecular-weight target detection by implementing duplexed aptamers on an FO-SPR sensor. In this manner, we enabled one-step competitive detection and could achieve significant signals, independent of the weight of the target molecules, without requiring labeling or preprocessing steps. This was demonstrated for the detection of a small molecule (ATP), protein (thrombin), and ssDNA target, thereby reaching detection limits of 72 μM, 36 nM, and 30 nM respectively and proving the generalizability of the proposed bioassay. Furthermore, target detection was successfully achieved in 10-fold diluted plasma, which demonstrated the applicability of the assay in biologically relevant matrices. Altogether, the developed one-step competitive FO-SPR bioassay opens up possibilities for the detection of low-molecular-weight targets in a fast and straightforward manner.

Harnessing selectivity in chemical sensing via supramolecular interactions: from functionalization of nanomaterials to device applications

Chemical sensing is a strategic field of science and technology ultimately aiming at improving the quality of our lives and the sustainability of our Planet. Sensors bear a direct societal impact on well-being, which includes the quality and composition of the air we breathe, the water we drink, and the food we eat. Pristine low-dimensional materials are widely exploited as highly sensitive elements in chemical sensors, although they suffer from lack of intrinsic selectivity towards specific analytes. Here, we showcase the most recent strategies on the use of (supra)molecular interactions to harness the selectivity of suitably functionalized 0D, 1D, and 2D low-dimensional materials for chemical sensing. We discuss how the design and selection of receptors via machine learning and artificial intelligence hold a disruptive potential in chemical sensing, where selectivity is achieved by the design and high-throughput screening of large libraries of molecules exhibiting a set of affinity parameters that dictates the analyte specificity. We also discuss the importance of achieving selectivity along with other relevant characteristics in chemical sensing, such as high sensitivity, response speed, and reversibility, as milestones for true practical applications. Finally, for each distinct class of low-dimensional material, we present the most suitable functionalization strategies for their incorporation into efficient transducers for chemical sensing.

Rapid and selective detection of aluminum ion using 1,2,3-triazole-4,5-dicarboxylic acid-functionalized gold nanoparticle-based colorimetric sensor

A highly selective, sensitive, rapid, low-cost, simple and visual colorimetric system for Al3+ ion detection was developed based on gold nanoparticles (AuNPs) modified with 1,2,3-triazole-4,5-dicarboxylic acid (TADA). The modified gold nanoparticles (TADA-AuNPs) were first prepared by sodium citrate (Na3Ct) reduction of chloroauric acid (HAuCl4) and then capped with a TADA ligand. Five TADA-AuNPs sensors were constructed with sodium citrate (Na3Ct)/chloroauric acid (HAuCl4) under different molar ratios. Results showed that the molar ratio of Na3Ct/HAuCl4, TADA-AuNPs concentration, pH range and detection time had obvious influences on the performance of this colorimetric method. The optimal detection conditions for Al3+ ions were as follows: Na3Ct/HAuCl4 molar ratio of 6.4 : 1, 0.1 mM of TADA-AuNPs concentration, 4-10 pH range and 90 s of detection time. Under the optimal conditions and using diphenyl carbazone (DPC) as a Cr3+ masking agent, this colorimetric sensor exhibited outstanding time efficiency, selectivity and sensitivity for Al3+ detection. In particular, the detection limits of this sensor obtained via UV-vis and the naked eye were 15 nM and 1.5 μM, respectively, which were much lower than the current limit (3.7 μM) for drinking water in WHO regulation and better than the previous reports. Moreover, this colorimetric sensing system could be used to for on-site, trace level and real-time rapid detection of Al3+ in real water samples.

Glutathione-functionalized long-period fiber gratings sensor based on surface plasmon resonance for detection of As3+ ions

Development of simple and accurate methods for the detection of As³⁺is highly desirable and technically important. In this work, a highly sensitive and selective long-period fiber gratings sensor based on surface plasmon resonance was developed for As³⁺detection by designing glutathione-functionalized Au nanoparticles as a signal amplification tag. Based on the chemical interaction between As³⁺and glutathione, the self-assembling glutathione on the surface of the gold film combines selectively with As³⁺, and then anchors the glutathione-functionalized Au nanoparticles, which changes the refractive index of the surrounding environment, resulting in a shift of the transmission spectrum. Results show that the sensor could detect As³⁺with concentrations ranging from 0.02 to 2 ppb. The sensor exhibited excellent specificity for As³⁺against other metal ions, such as Na⁺, Fe³⁺, Mg²⁺, Cu²⁺, Pb²⁺, Ni²⁺, Ba²⁺, and Co³⁺. The fiber sensor was successfully employed to detect As³⁺in pond water samples, demonstrating that it has the potential for As³⁺detection with the advantages of low cost, high sensitivity, and a simple structure.

Highly sensitive detection of Hg2+ employing SPR sensor modified with chitosan/poly (vinyl alcohol)/SnO2 film

Water contamination by mercury ions (Hg²⁺) causes irreversible and serious effect on the ambient environment, ecological systems, and human health, necessitating further improvement of Hg²⁺ monitoring at low concentrations. Here, we proposed a novel surface plasmon resonance (SPR) sensor for Hg²⁺ detection with desirable advantages of high sensitivity, simple operation, label-free, and low cost, in which the chitosan/poly (vinyl alcohol)/SnO₂ composite film was modified on sensing surface as the active layer for sensitivity enhancement. Benefiting from the relatively high refractive index of SnO₂ nanoparticles, the evanescent field generated at the metal-solution interface can be significantly enhanced, which results in a 5 times improvement of sensitivity. Through appropriate optimization in the aspects of componential constitutions, the sensor exhibits excellent sensitivity of 25.713 nm/μg/L and ultra-low calculated detection limit of 6.61 ng/L(32.95 pM). Such detection limit is strikingly lower than the limitation (10 nM) in drinking water set by the US Environmental Protection Agency. In addition, the as-prepared sensor presents relatively high selectivity for Hg²⁺, attributing to plenty of binding sites for specific adsorption produced by functionalized chitosan/poly (vinyl alcohol) composites, which have been furtherly verified by characterization of FTIR and XPS spectra. The proposed sensor also exhibits great repeatability and good time stability for 15 days. This work provides a promising strategy for developing high-performance SPR sensor for Hg²⁺ detection and a prospective application in environmental monitoring.

Two-dimensional nano-layered materials as multi-responsive chemosensors constructed by carbazole- and fluorene-based polyaniline-like derivatives

The development of multi-responsive chemosensors has a bright application prospect in environmental monitoring and biological diagnosis. In this paper, we report two kinds of fluorescent polyaniline-like derivatives containing of carbazole or fluorene moieties with two-dimensional (2D) nano-layered structure and their applications in the detection of Al³⁺, Fe³⁺, Cu²⁺ and HCl in different environments. Through the analysis of the structure and properties of these two 2D materials, we find that the prepared (Poly(9,9'-(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(9H-carbazol-3-amine))) PDFCA material performs excellent sensing properties for above analytes. Relevant density functional theory (DFT) calculation further confirms the potential application of 2D nano-layered PDFCA material in sensing field. This study presents that 2D nano-layered PDFCA material is considerably competitive in the development of multi-responsive chemosensors, and it will greatly accelerate the research of 2D polymer materials.

Surface-Enhanced Raman Scattering Optophysiology Nanofibers for the Detection of Heavy Metals in Single Breast Cancer Cells

Mercury(II) ions (Hg²⁺) and silver ions (Ag⁺) are two of the most hazardous pollutants causing serious damage to human health. Here, we constructed surface-enhanced Raman scattering (SERS)-active nanofibers covered with 4-mercaptopyridine (4-Mpy)-modified gold nanoparticles to detect Hg²⁺ and Ag⁺. Experimental evidence suggests that the observed spectral changes originate from the combined effect of (i) the coordination between the nitrogen on 4-Mpy and the metal ions and (ii) the 4-Mpy molecular orientation (from flatter to more perpendicular with respect to the metal surface). The relative intensity of a pair of characteristic Raman peaks (at ∼428 and ∼708 cm^-1) was used to quantify the metal ion concentration, greatly increasing the reproducibility of the measurement compared to signal-on or signal-off detection based on a single SERS peak. The detection limit of this method for Hg²⁺ is lower than that for the Ag⁺ (5 vs 100 nM), which can be explained by the stronger interaction energy between Hg²⁺ and N compared to Ag⁺ and N, as demonstrated by density functional theory calculations. The Hg²⁺ and Ag⁺ ions can be masked by adding ethylenediaminetetraacetate and Cl^-, respectively, to the Hg²⁺ and Ag⁺ samples. The good sensitivity, high reproducibility, and excellent selectivity of these nanosensors were also demonstrated. Furthermore, detection of Hg²⁺ in living breast cancer cells at the subcellular level is possible, thanks to the nanometric size of the herein described SERS nanosensors, allowing high spatial resolution and minimal cell damage.

Ultra-sensitive reusable SERS sensor for multiple hazardous materials detection on single platform

We demonstrate the detection of dipicolinic acid, (DPA), a biomarker of bacterial spores for Bacillus anthracis, 2,4-Dinitrotoluene (DNT) and picric acid (PA) nitroaromatic hazardous chemicals on ultra-sensitive, reusable femtosecond laser textured Au nanostructures decorated with hierarchical AuNPs as a SERS substrate. The AuNPs were achieved by ablating an Au sheet using two different laser scan speeds (1 and 0.1 mm/s) in linear and crossed patterns. The morphological studies revealed dense hierarchical nanostructures decorated with spherical AuNPs possessing 30-40 nm in size in 0.1 mm/s laser scan. The limits of detection (LOD) of the sensor were determined from the detailed SERS measurements and were estimated to be 0.83 pg/L, 3.6 pg/L and 2.3 pg/L for DPA, DNT, and PA, respectively. To the best of our knowledge, the achieved sensitivity is nearly 2 orders improved for DPA when compared with the currently reported LODs using other techniques and 1 order in the case of SERS. Moreover, for DNT and PA the LODs were found to be either superior or comparable with recent reports. We have also demonstrated the competence of our SERS substrates by testing a few real samples (water spiked with these analytes) and again obtained very good sensitivity.

Thymine-Functionalized Gold Nanoparticles (Au NPs) for a Highly Sensitive Fiber-Optic Surface Plasmon Resonance Mercury Ion Nanosensor

Mercury ion (Hg²⁺) is considered to be one of the most toxic heavy metal ions. Once the content of Hg²⁺ exceeds the quality standard in drinking water, the living environment and health of human beings will be threatened and destroyed. Therefore, the establishment of simple and efficient methods for Hg²⁺ ion detection has important practical significance. In this paper, we present a highly sensitive and selective fiber-optic surface plasmon resonance (SPR) Hg²⁺ ion chemical nanosensor by designing thymine (T)-modified gold nanoparticles (Au NPs/T) as the signal amplification tags. Thymine-1-acetic acid (T-COOH) was covalently coupled to the surface of 2-aminoethanethiol (AET)-modified Au NPs and Au film by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride/N-Hydroxysuccinimide (EDC/NHS) activation effect, respectively. In the presence of Hg²⁺ ions, the immobilized thymine combines specifically with Hg²⁺ ions, and forms an Au/thymine-Hg²⁺-thymine/Au (Au/T-Hg²⁺-T/Au) complex structure, leading to a shift in SPR wavelength due to the strong electromagnetic couple between Au NPs and Au film. Under optimal conditions, the proposed sensor was found to be highly sensitive to Hg²⁺ in the range of 80 nM–20 µM and the limit of detection (LOD) for Hg²⁺ was as low as 9.98 nM. This fiber-optic SPR sensor afforded excellent selectivity for Hg²⁺ ions against other heavy metal ions such as Fe³⁺, Cu²⁺, Ni²⁺, Ba²⁺, K⁺, Na⁺, Pb²⁺, Co²⁺, and Zn²⁺. In addition, the proposed sensor was successfully applied to Hg²⁺ assay in real environmental samples with excellent recovery. Accordingly, considering its simple advantages, this novel strategy provides a potential platform for on-site determination of Hg²⁺ ions by SPR sensor.

Recent advances in visual detection for cancer biomarkers and infectious pathogens

It is an urgency to detect infectious pathogens or cancer biomarkers using rapid, simple, convenient and cost-effective methods in complex biological samples. Many existing approaches (traditional virus culture, ELISA or PCR) for the pathogen and biomarker assays face several challenges in the clinical applications that require lengthy time, sophisticated sample pre-treatment and expensive instruments. Due to the simple and rapid detection manner as well as no requirement of expensive equipment, many visual detection methods have been considered to resolve the aforementioned problems. Meanwhile, various new materials and colorimetric/fluorescent methods have been tried to construct new biosensors for infectious pathogens and biomarkers. However, the recent progress of these aspects is rarely reviewed, especially in terms of integration of new materials, microdevice and detection mechanism into the visual detection systems. Herein, we provide a broad field of view to discuss the recent progress in the visual detection of infectious pathogens and cancer biomarkers along with the detection mechanism, new materials, novel detection methods, special targets as well as multi-functional microdevices and systems. The novel visual approaches for the infectious pathogens and biomarkers, such as bioluminescence resonance energy transfer (BRET), metal-induced metallization and clustered regularly interspaced short palindromic repeats (CRISPR)-based biosensors, are discussed. Additionally, recent advancements in visual assays utilizing various new materials for proteins, nucleic acids, viruses, exosomes and small molecules are comprehensively reviewed. Future perspectives on the visual sensing systems for infectious pathogens and cancers are also proposed.

Effects of cellulose/salicylaldehyde thiosemicarbazone complexes on PVA based hydrogels: Portable, reusable, and high-precision luminescence sensing of Cu2

Novel portable, high-precision, and reusable fluorescent polyvinyl alcohol (PVA)-borax hydrogel sensors were prepared to detect Cu²⁺ in aqueous environment. A TEMPO-oxidized cellulose nanofibers/salicylaldehyde thiosemicarbazone (TOCN/ST) complex was further incorporated into the PVA-borax matrix. The in situ polymerization of TOCN/ST complex enhanced the mechanical properties of the hydrogels and improved the accuracy of detection. The resultant hydrogels were thermo reversible, and it converted to the liquid state during heating, which could greatly reduce the deviations caused in the detection of solid sensors. After cooling, the hydrogel could transform into the solid condition, which was easily portable. The sensor induced a significant luminescence quenching to the Cu²⁺ at 485 nm, with a detection limit of 0.086 μM. In the presence of ethylenediaminetetraacetic acid disodium, Cu²⁺ were tightly seized, causing the liberation of TOCN/ST complex and thus, a reversible "ON-OFF-ON" fluorescence behavior was displayed. The fluorescence intensity was maintained at 82 % after 10 uses, and the mechanical strength was maintained at 85 % after 3 uses. The anti-bacterial activity test also confirmed the TOCN/ST complex was extremely potent in suppressing the growth and reproduction of Escherichia coli. The proposed hydrogel provides a new insight into the detection of Cu²⁺ in aqueous environments.

Metal-Organic Framework-Plant Nanobiohybrids as Living Sensors for On-Site Environmental Pollutant Detection

Photoluminescent metal-organic frameworks (MOFs) were grown in a living plant (Syngonium podophyllum) via immersing their roots in an aqueous solution of disodium terephthalate and terbium chloride hexahydrate sequentially for 12 h without affecting their viability. Then, app-assisted living MOF-plant nanobiohybrids were used for the detection of various toxic metal ions and organic pollutants. Their performance and sensing mechanism were also evaluated. The results demonstrated that the living plants served as self-powered preconcentrators via their passive fluid transport systems and accumulated the pollutants around the embedded MOFs, resulting in relative changes in fluorescence intensity. Therefore, the living MOF-plant nanobiohybrids initiate superior selectivity and sensitivity (0.05-0.5 μM) in water for Ag⁺, Cd²⁺, and aniline with a "turn-up" fluorescence response and for Fe³⁺ and Cu²⁺ with "turn-down" fluorescence response in the linear range of 0.05-10 μM with excellent precision and accuracy of 5 and 10%, respectively. With the easy-to-read visual signals under ultraviolet light, the app translates plant luminescent signals into digital information on a smartphone for on-site monitoring of environmental pollutants with high sensitivity and specificity. These results suggest that interfacing synthetic and living materials may contribute to the development of smart sensors for on-site environmental pollutant sensing with high accuracy.

Preparation and Application of Metal Nanoparticals Elaborated Fiber Sensors

In recent years, surface plasmon resonance devices (SPR, or named plamonics) have attracted much more attention because of their great prospects in breaking through the optical diffraction limit and developing new photons and sensing devices. At the same time, the combination of SPR and optical fiber promotes the development of the compact micro-probes with high-performance and the integration of fiber and planar waveguide. Different from the long-range SPR of planar metal nano-films, the local-SPR (LSPR) effect can be excited by incident light on the surface of nano-scaled metal particles, resulting in local enhanced light field, i.e., optical hot spot. Metal nano-particles-modified optical fiber LSPR sensor has high sensitivity and compact structure, which can realize the real-time monitoring of physical parameters, environmental parameters (temperature, humidity), and biochemical molecules (pH value, gas-liquid concentration, protein molecules, viruses). In this paper, both fabrication and application of the metal nano-particles modified optical fiber LSPR sensor probe are reviewed, and its future development is predicted.

Cardiac troponin I photoelectrochemical sensor: {Mo368} as electrode donor for Bi2S3 and Au co-sensitized FeOOH composite

A suitable electron donor, which guarantees the stability of the whole system, is considered as the driving force of the PEC sensor. Nowadays, searching appropriate electron donor is still one of the orientations to explorate in the field of sensor. Na₄₈[H₄₉₆Mo₃₆₈O₁₄₆₄S₄₈]·ca.1000H₂O (abbr. {Mo₃₆₈}), as a type of polyoxometalate, has perfect morphology, definite size and unique electronic property. Due to the prominent water solubility, {Mo₃₆₈} usually releases small cations and exists as large anions in the ultrapure water. The interesting property endows {Mo₃₆₈} with excellent reducibility, which provides great feasibility to become an outstanding electron donor. In addition, FeOOH prepared through a simple operation owns high adsorption capacity, which ensures the fastness of other materials. Subsequently, the narrow band-gap of Bi₂S₃ and the unique noble metal properties of Au nanoparticles are utilized to co-sensitize FeOOH to improve the light-harvesting capability and photoelectric conversion efficiency. Combined with the specificity recognition of antigen and antibody, a novel photoelectrochemical sensor is constructed with a wide detection range of 1.00 pg mL^-1 - 100 ng mL^-1 and low detection limit (0.76 pg mL^-1), which achieves the sensitive detection of cardiac troponin I in early diagnosis of cardiovascular disease.

Portable and field-deployed surface plasmon resonance and plasmonic sensors

Plasmonic sensors are ideally suited for the design of small, integrated, and portable devices that can be employed in situ for the detection of analytes relevant to environmental sciences, clinical diagnostics, infectious diseases, food, and industrial applications. To successfully deploy plasmonic sensors, scaled-down analytical devices based on surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) must integrate optics, plasmonic materials, surface chemistry, fluidics, detectors and data processing in a functional instrument with a small footprint. The field has significantly progressed from the implementation of the various components in specifically designed prism-based instruments to the use of nanomaterials, optical fibers and smartphones to yield increasingly portable devices, which have been shown for a number of applications in the laboratory and deployed on site for environmental, biomedical/clinical, and food applications. A roadmap to deploy plasmonic sensors is provided by reviewing the current successes and by laying out the directions the field is currently taking to increase the use of field-deployed plasmonic sensors at the point-of-care, in the environment and in industries.