Trace Detection Research Articles

1ppm-detectable hydrogen gas sensors by using highly sensitive P+/N+ single-crystalline silicon thermopiles

Hydrogen (H2) is currently of strategic importance in the pursuit of a decarbonized, environmentally benign, sustainable global energy system; however, the explosive nature of H2 requires leakage monitoring to ensure safe application in industry. Therefore, H2 gas sensors with a high sensitivity and fast response across a wide concentration range are crucial yet technically challenging. In this work, we demonstrate a new type of MEMS differential thermopile gas sensor for the highly sensitive, rapid detection of trace H2 gas in air. Facilitated by a unique MIS fabrication technique, pairs of single-crystalline silicon thermopiles (i.e., sensing and reference thermopiles) are batch fabricated with high-density single-crystalline silicon thermocouples, yielding an outstanding temperature sensitivity at the sub-mK level. Such devices ensure the detection of miniscule temperature changes due to the catalytic reaction of H2 with a detection limit as low as ~1 ppm at an operating temperature of 120 °C. The MEMS differential thermopiles also exhibit a wide linear detection range (1 ppm-2%, more than four orders of magnitude) and fast response and recovery times of 1.9 s and 1.4 s, respectively, when detecting 0.1% H2 in air. Moreover, the sensors show good selectivity against common combustible gases and volatile organics, good repeatability, and long-term stability. The proposed MEMS thermopile H2 sensors hold promise for the trace detection and early warning of H2 leakage in a wide range of applications.

Highly Sensitive Capacitive MEMS for Photoacoustic Gas Trace Detection.

An enhanced MEMS capacitive sensor is developed for photoacoustic gas detection. This work attempts to address the lack of the literature regarding integrated and compact silicon-based photoacoustic gas sensors. The proposed mechanical resonator combines the advantages of silicon technology used in MEMS microphones and the high-quality factor, characteristic of quartz tuning fork (QTF). The suggested design focuses on a functional partitioning of the structure to simultaneously enhance the collection of the photoacoustic energy, overcome viscous damping, and provide high nominal capacitance. The sensor is modeled and fabricated using silicon-on-insulator (SOI) wafers. First, an electrical characterization is performed to evaluate the resonator frequency response and nominal capacitance. Then, under photoacoustic excitation and without using an acoustic cavity, the viability and the linearity of the sensor are demonstrated by performing measurements on calibrated concentrations of methane in dry nitrogen. In the first harmonic detection, the limit of detection (LOD) is 104 ppmv (for 1 s integration time), leading to a normalized noise equivalent absorption coefficient (NNEA) of 8.6 ⋅ 10-8 Wcm-1 Hz-1/2, which is better than that of bare Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS), a state-of-the-art reference to compact and selective gas sensors.

Calculating the Limits of Detection in Laser-Induced Breakdown Spectroscopy: Not as Easy as It Might Seem

The objectives of this paper will be to discuss the issues related to the determination of the limits of detection (LOD) in laser-induced breakdown spectroscopy (LIBS) analytical applications. The derivation of the commonly used ‘3-sigma over slope’ rule and its evolution towards the new official definition recently adopted by the International Union of Pure and Applied Chemistry (IUPAC) will be illustrated. Methods for extending the calculation of the LOD to LIBS multivariate analysis will also be discussed, using as an example the detection of Cu traces in cast iron samples by LIBS.

Subppb level monitoring and UV degradation of triclosan pollutants using ZnO multipod and Ag nanocomposites

A unique nanomaterial platform was developed for trace detection and efficient degradation of triclosan (TCS). A facile spectroscopic technique for surface-enhanced Raman scattering (SERS)-supported identification and ultraviolet (UV) degradation of TCS using a SERS template based on silver spherical nanoparticle (AgNP)-modified ZnO multipods (ZnO@Ag) is reported. Core-shell composite materials of ZnO multipods with a dimension of around 3 μm and AgNPs with an average diameter of ∼27 nm was designed not only as a substrate for TCS degradation up to ∼92% upon UV irradiation (λ = 365 mm, 300 μW/cm2) but also as a monitoring platform sensitive to TCS at a detection limit as low as 10−9 M (≈0.3 ppb). Herein, the first investigation into ZnO@Ag bimetallic composites is established for both the SERS-based detection and UV-assisted degradation of environmental TCS pollutants. The calibration curve was estimated to be linear at R2 > 0.97. The validated technology was successfully used to determine the antibacterial agent and TCS in distilled or river water. The advantages of the ZnO@Ag template are highlighted over conventional detection and excellent degradation.

A highly sensitive and selective photoelectrochemical aptasensor for atrazine based on Au NPs/3DOM TiO2 photonic crystal electrode

A photoelectrochemical (PEC) sensing platform with high sensitivity and selectivity has been fabricated based on Au nanoparticles (Au NPs) modified three dimensionally ordered macroporous (3DOM) TiO2 nanostructure frame for trace detection of an endocrine disrupting pesticide, atrazine (ATZ). The resultant photoanode (Au NPs/3DOM TiO2) shows enhanced PEC performance under visible light due to multi signal amplification of the unique structure of 3DOM TiO2 and surface plasmon resonance (SPR) of Au NPs. ATZ aptamers are used as recognition elements and immobilized on Au NPs/3DOM TiO2 by Au-S bond in large packing density and dominant spatial orientation. The specific recognition and high binding affinity between aptamer and ATZ provides the PEC aptasensor with excellent sensitivity. The detection limit is 0.167 ng/L. Besides, this PEC aptasensor exhibits outstanding anti-interference ability in 100-fold concentration of other endocrine disrupting compounds and has been applied successfully to analyze ATZ in real water samples. A simple but efficient PEC aptasensing platform has therefore been successfully developed with high sensitivity, selectivity and repeatability for pollutant monitoring and potential risk evaluation in the environment with great application prospect.

Red-emissive carbon dots based fluorescent and smartphone-integrated paper sensors for sensitive detection of carbendazim

Trace detection of carbendazim (CBZ), a worldwide used pesticide, in crops and foods is important and urgent to reduce risks to human health. Herein, newly red-emissive carbon dots (R-CDs) based fluorescent and smartphone-integrated paper sensors were developed for highly-selective, and -sensitive rapid sensing of CBZ. R-CDs were synthesized from citric acid and urea via a DMF solvothermal method, which showed excellent analytical performance due to abundant carboxyl groups on the surface and long emission wavelength to avoid autofluorescence interference of matrix. According to the red fluorescence quenching by CBZ via π-π interaction and photoinduced electron-transfer effect, the newly fluorescent nano sensor could realize CBZ sensing within 3 min with high selectivity out of the other six interfering pesticides, as well as fascinating sensitivity with an ultralow detection limit of 3.5 ng/mL. The practicable application in the spiked medicinal Lotus seeds samples exhibited satisfactory recoveries of 95.5%-108.3%. The portable paper-based sensor fabricated by depositing R-CDs on the filter paper enabled quantitative readout of test strip results assisted with a smartphone, providing a rapid on-site tool for CBZ detection in medicinal foods. This is the first report of a novel, sensitive, and portable R-CDs based sensing platform for simple, cost-effective, and rapid on-site detection of CBZ in the field of food safety with great application potential.

Plasmonic Coupling of Au Nanoclusters on a Flexible MXene/Graphene Oxide Fiber for Ultrasensitive SERS Sensing.

High sensitivity, good signal repeatability, and facile fabrication of flexible surface enhanced Raman scattering (SERS) substrates are common pursuits of researchers for the detection of probe molecules in a complex environment. However, fragile adhesion between the noble-metal nanoparticles and substrate material, low selectivity, and complex fabrication process on a large scale limit SERS technology for wide-ranging applications. Herein, we propose a scalable and cost-effective strategy to a fabricate sensitive and mechanically stable flexible Ti3C2Tx MXene@graphene oxide/Au nanoclusters (MG/AuNCs) fiber SERS substrate from wet spinning and subsequent in situ reduction processes. The use of MG fiber provides good flexibility (114 MPa) and charge transfer enhancement (chemical mechanism, CM) for a SERS sensor and allows further in situ growth of AuNCs on its surface to build highly sensitive hot spots (electromagnetic mechanism, EM), promoting the durability and SERS performance of the substrate in complex environments. Therefore, the formed flexible MG/AuNCs-1 fiber exhibits a low detection limit of 1 × 10-11 M with a 2.01 × 109 enhancement factor (EFexp), signal repeatability (RSD = 9.80%), and time retention (remains 75% after 90 days of storage) for R6G molecules. Furthermore, the l-cysteine-modified MG/AuNCs-1 fiber realized the trace and selective detection of trinitrotoluene (TNT) molecules (0.1 μM) via Meisenheimer complex formation, even by sampling the TNT molecules at a fingerprint or sample bag. These findings fill the gap in the large-scale fabrication of high-performance 2D materials/precious-metal particle composite SERS substrates, with the expectation of pushing flexible SERS sensors toward wider applications.

A simple and efficient strategy for trace detection of ferroptosis-related miRNAs based on novel hydrophobic paper-based plasmonic substrate and "inverse molecular sentinel (iMS)" nanoprobes.

Monitoring ferroptosis-related miRNAs is crucial for the treatment and prognosis of patients with intracerebral hemorrhage. In this work, a novel hydrophobic paper (h-paper)-based plasmonic substrate was produced by dropping DS Au nanorods with a narrow range of sizes and morphologies onto h-paper. Raman reporter molecules were adsorbed to the array surface, and surface-enhanced Raman scattering spectra at randomly selected points reveal uniform and significant SERS enhancement. Hairpin DNAs labelled with Raman reporters and hybridized with placeholder DNAs were decorated on SERS substrate to fabricate SERS biosensor. Target miRNAs initiated the "inverse Molecular Sentinel" process. During the process, PHs were removed and the conformation of HPs changed toward the hairpin structure, thus eliciting the proximity of Raman reporter to substrate and a stronger SERS signal. The proposed SERS biosensor performs well in terms of stability, reproducibility, and selectivity. The limits of detection of miR-122-5p and miR-140-5p in serum were 4.17 aM and 4.49 aM, respectively. Finally, the fabricated SERS biosensor was applied to detect miR-122-5p and miR-140-5p in ICH patients and healthy subjects, and the results obtained by SERS were consistent with the results from quantitative real-time polymerase chain reaction, revealing the accuracy of the method. This simple, rapid approach offers great potential for the simultaneous detection of miRNAs in practical clinical applications.

Humidity-independent electronic nose of α-Fe2O3/ZnFe2O4 heterojunctions for trace detection of N-butanol exhalation in lung cancer screening

Magnetic metal oxide semiconductors (MOSs) are emerging gas-sensing materials. Most researches were devoted to monitoring large-scale gases in industrial emissions, but the trace detection of electronic noses applied in health diagnosis was always ignored. Herein, the humidity-independent α-Fe2O3/ZnFe2O4 (FZFO) heterojunctions with strong magnetism for N-butanol gas detection were prepared. They may potentially act as electronic noses in early lung cancer screening. This magnetism can endow FZFO to capture more oxygen for redox, and the n-n heterojunctions generated can significantly enhance gas sensitivity, improving the response even under 0.1 ppm at 160 ℃. Furthermore, the limit of detection of the FZFO-4 sample can reach 1 ppb, completely meeting the accuracy requirements. Notably, the humidity independence of FZFO-2 and FZFO-4 samples could maintain at relative humidity 91%, so they will hardly be influenced by water vapor exhaled from patients' mouths. This work first proposed the electronic nose of FZFO heterojunctions in lung cancer screening, which may initiate a wave of non-invasive diagnosis.

Recent Trends in SERS-Based Plasmonic Sensors for Disease Diagnostics, Biomolecules Detection, and Machine Learning Techniques.

Surface-enhanced Raman spectroscopy/scattering (SERS) has evolved into a popular tool for applications in biology and medicine owing to its ease-of-use, non-destructive, and label-free approach. Advances in plasmonics and instrumentation have enabled the realization of SERS's full potential for the trace detection of biomolecules, disease diagnostics, and monitoring. We provide a brief review on the recent developments in the SERS technique for biosensing applications, with a particular focus on machine learning techniques used for the same. Initially, the article discusses the need for plasmonic sensors in biology and the advantage of SERS over existing techniques. In the later sections, the applications are organized as SERS-based biosensing for disease diagnosis focusing on cancer identification and respiratory diseases, including the recent SARS-CoV-2 detection. We then discuss progress in sensing microorganisms, such as bacteria, with a particular focus on plasmonic sensors for detecting biohazardous materials in view of homeland security. At the end of the article, we focus on machine learning techniques for the (a) identification, (b) classification, and (c) quantification in SERS for biology applications. The review covers the work from 2010 onwards, and the language is simplified to suit the needs of the interdisciplinary audience.

An ultrasensitive split-type electrochemical immunosensor based on controlled-release strategy for detection of CA19-9

In this study, a novel split-type electrochemical immunosensor based on controlled release strategy was proposed for sensitive analysis and detection of tumor marker carbohydrate antigen 199 (CA19-9). Specifically, glucose (Glu) was encapsulated in carrier mesoporous silica (MSN) with encapsulation technology, and surface functionalized Zinc sulfide (ZnS) caps were used as “gatekeepers”. The complex is formed by encapsulating Glu within MSN with ZnS (ZnS@MSN-Glu) as a signal amplifier labeled on the signal antibody (Ab2). And the Ab2 can detect the presence of antibodies. To reduce the interference of biological analysis, the immune recognition process of ZnS@MSN-Glu-Ab2 bioconjugate and antigen was carried out in 96-well microplate, which did not interfere with the electrochemical analysis process. Therefore, the low sensitivity detection caused by biofouling of nanomaterials and immunoreaction on the testing platform is eliminated. Subsequently, the opening and timed release of mesopores were controlled by external stimuli, the disulfide bond cleavage by dithiothreitol (DTT), and glucose was effectively released. Then nickel cobalt layered double hydroxide (NiCo-LDH) were directly hydrothermally grown on carbon cloth (CC) electrodeposited with copper selenide (CuSe) nanosheets to construct three-dimensional (3D) cactus-like NiCo-LDH/CuSe/CC sensing platform. It can realize the catalytic oxidation of released glucose, triggering glucose-mediated signal amplification. The synergistic effect of the 3D cactus structure and active nanomaterials promotes electron conduction. Taking the detection of carbohydrate antigen CA19-9 as an example, the immunosensor shows a wide linear concentration range (0.001–100 U/mL) with the limit of detection of 0.0005 U/mL, realizing highly sensitive detection of CA19-9. This biosensing technique has considerable advantages and provides an innovative approach for trace detection of other biomarkers.

The identification of synthetic cannabinoids in English prisons

Synthetic cannabinoids (SC) are extremely prevalent within the prison system and cause problems for prisoners, law enforcement and health services. SC are often soaked into paper then posted into prisons therefore one of the aims of this research is to collaborate with Rapiscan Systems Ltd. and local prisons in England to measure the effectiveness of trace detection methods for the indication of SC in prison post using the Itemiser 3E®. To ensure compounds did not go undetected, samples with Ion Trap Mobility Spectrometry™ peaks indicative of synthetic cannabinoids on the Itemiser 3E® were analysed using Gas Chromatography-Mass Spectrometry, Liquid Chromatography-Quadrupole Time-of-Flight Mass Spectrometry and Nuclear Magnetic Resonance Spectroscopy to identify chemical characteristics which allowed comparison to reference spectra. Sample data spanning three years from one prison’s Itemiser 3E® were collated to identify trends in drug prevalence and the influence of library updates. To date, the method has identified four compounds: 5F‐MDMB‐PICA, MMB-4en-PICA, 4F‐MDMB‐BUTINACA and MDMB-4en-PINACA on prison post which were not already included on, or needed confirmatory analysis to update, the Itemiser 3E® library. As a result, the libraries on prison Itemiser 3E®s have been updated to ensure future detection of such compounds. Trends and influences from the processed Itemiser 3E® data were also reported back to the West Midlands Prison Group. This research directly benefitted both the West Midlands Prison Group and Rapiscan Systems Ltd. and it is anticipated that the continuation of this research could be expanded to a national scale.

High-sensitivity polarization-independent terahertz Taichi-like micro-ring sensors based on toroidal dipole resonance for concentration detection of Aβ protein

Abstract Terahertz (THz) metamaterial sensor is a newly-developing interdisciplinary technology, which combines the essential characteristics of THz spectroscopy and metamaterials, to obtain better sensitivity for trace detection of the different target analytes. Toroidal dipole resonances show great sensing potential due to their suppression of the radiative loss channel. Here, we found a high-quality planar toroidal dipole resonance in the breaking Chinese Taichi-like ring and then designed a novel polarization-independent terahertz toroidal sensor by combining four Taichi-like rings into a cycle unit. The sensor shows high-sensitivity sensing characteristics for the ultrathin analyte and refractive index. The optimized sensitivity of pure analytes under 4 μm coating thickness can numerically reach 258 GHz/RIU in the corresponding ∼1.345 THz frequency domain, which is much higher than that of previously reported sensors. We further fabricated experimentally the sensor and demonstrated its fascinating polarization-independent characteristics. Finally, it was successfully applied to the low-concentration detection (ranging from 0.0001 mg/mL to 10 mg/mL) of Aβ protein associated with Alzheimer’s disease. Our high-sensitivity polarization-independent THz toroidal dipole sensor would give access to rich applications in label-free biosensing.

Hydrogels: From Design to Applications in Forensic Investigations

AbstractThe concept of green hydrogels in forensics is a budding area where it encompasses the concept of sustainable investigation. Motivated by the need to prepare for the next generation advanced materials for implementing proactive forensic science strategy. The work conception, already successful in a few fields, aimed at implementing the sophisticated criminal's way of thinking, predicting their next move so that the crime‐fighting authorities can be one step ahead of them and take precautionary actions. The existing problems of current society need to be solved by deliberate efforts of researchers and forensic experts, as we can formulate strategy of design, production, and characterization of innovative polymeric materials for on spot detection of traces. Various innovative materials have been explored with the help of green chemistry. Fingerprinted products that are unique in their compilation are made in forensics by utilizing the concept of green chemistry. The creation of nontoxic hydrogels by utilizing green polymers that are biodegradable, biocompatible, and bio renewable is one such field that helps in forensic applications. The distinctive properties of hydrogels make them suitable for various forensic investigations. In this review article, we have focused on the unique sparked properties of these smart gels and opened a gateway in solving various unsolved mysteries.

Construction of Flower-like PtOx@ZnO/In2O3 Hollow Microspheres for Ultrasensitive and Rapid Trace Detection of Isopropanol.

The design of a highly effective isopropanol gas sensor with high response and trace detection capability is extremely important for environmental surveillance and human health. Here, novel flower-like PtOx@ZnO/In2O3 hollow microspheres were prepared by a three-step approach. The hollow structure was composed of an In2O3 shell inside and layered ZnO/In2O3 nanosheets outside with PtOx nanoparticles (NPs) on the surface. Meanwhile, the gas sensing performances of the ZnO/In2O3 composite with different Zn/In ratios and PtOx@ZnO/In2O3 composites were evaluated and compared systematically. The measurement results indicated that the ratio of Zn/In affected the sensing performance and the ZnIn2 sensor presented a higher response, which was then modified with PtOx NPs to further enhance its sensing property. The Pt@ZnIn2 sensor exhibited outstanding isopropanol detection performance with ultrahigh response values under 22 and 95% relative humidity (RH). In addition, it also showed a rapid response/recovery speed, good linearity, and low theoretical limit of detection (LOD) regardless of being under a relatively dry or ultrahumid atmosphere. The enhancement of isopropanol sensing properties might be ascribed to the unique structure of PtOx@ZnO/In2O3, heterojunctions between the components, and catalytic effect of Pt NPs.

Toward surface-enhanced Raman scattering using electroless substrate for trace arsenic detection and speciation

Arsenic is one of the most toxic elements present in the environment, especially in water. The World Health Organization (WHO) recommends a maximum concentration of arsenic in drinkable water of 10 μg/l (10 ppb). Sensors implementing Surface Enhanced Raman Scattering (SERS) can detect chemical species at low concentrations. The aim of this study is to compare two kinds of silver-coated SERS substrates for detection and speciation of trace, trivalent and pentavalent, inorganic arsenic compounds. One type of substrate was prepared by a classical thermal evaporation technique, and the second type by an electroless process. The thermally evaporated substrates allowed the detection of As(III) only, at a limit of detection (LOD) of approximately 50 mg/l, whereas As(V) could not be detected at any analyte concentration. The electroless substrates allow one to differentiate As(III) and As(V) with a LOD 1 μg/l (1 ppb) equal for each valency, below the WHO recommendation. The electroless substrates show a very large sensitivity across up to five orders of magnitude in terms of analyte concentration. Although the SERS intensity shows a nonlinear behavior over this range of concentrations, these preliminary results are encouraging in the framework of the demonstration of trace As SERS sensors in drinkable water.

Construction of MOF@COF composite-based electrochemical aptasensor for detection of Staphylococcus aureus.

In this work, a biological metal-organic framework@conductive covalent organic framework composite (bio-MOF@con-COF, denoted as Zn-Glu@PTBD-COF, here, Glu indicates L-glutamic acid, PT indicates 1,10-phenanthroline-2,9-dicarbaldehyde, and BD indicates benzene-1,4-diamine) was prepared and used as sensing material to fabricate aptasensor for trace detection of Staphylococcus aureus (SA). The Zn-Glu@PTBD-COF integrates the mesoporous structure and abundant defects of the MOF framework, the excellent conductivity of the COF framework, and high stability of the composite, providing abundant active sites to effectively anchor aptamers. As a result, the Zn-Glu@PTBD-COF-based aptasensor shows high sensitivity to detect SA via specific recognition between aptamer and SA, as well as the formation of aptamer-SA complex. Low detection limits of 2.0 and 1.0CFU·mL-1 are deduced from the electrochemical impedance spectroscopy and differential pulse voltammetry within a wide linear range of 10-108CFU·mL-1 for SA, respectively. The Zn-Glu@PTBD-COF-based aptasensor also shows good selectivity, reproducibility, stability, regenerability, and applicability for real milk and honey samples. Therefore, the Zn-Glu@PTBD-COF-based aptasensor will be promising for fast screening of foodborne bacteria in food service industry. Zn-Glu@PTBD-COF composite was prepared and used as sensing material to fabricate aptasensor for trace detection of Staphylococcus aureus (SA). Low detection limits of 2.0 and 1.0CFU·mL-1 are deduced from the electrochemical impedance spectroscopy and differential pulse voltammetry within a wide linear range of 10-108CFU·mL-1 for SA, respectively. The Zn-Glu@PTBD-COF-based aptasensor also shows good selectivity, reproducibility, stability, regenerability, and applicability for real milk and honey samples.

Ratio fluorescence sensor based on CD/Cu-MOFs for detection of Hg2.

Trace detection of toxic heavy metals is a very important and difficult problem in several areas: convenience, sensitivity, and reliability. Herein, we develop an innovative fluorescence resonance energy transfer (FRET)-based ratio fluorescence sensor for the detection of heavy metal mercury ion (H g 2+). The sensing platform is composed of coumarin derivatives (CDs) and a copper metal-organic framework (Cu-MOF) named CD/Cu-MOF. The constructed CD/Cu-MOFs ratio fluorescence sensor exhibits dual emission peaks at 430 and 505nm under the single excitation wavelength of 330nm. With the addition of H g 2+, the fluorescence intensity of the system at 430nm gradually increased, and the fluorescence intensity at 505nm remained stable, resulting in a change in the fluorescence ratio. There is a good logarithmic relationship between the H g 2+ concentration in the range from 2×10-8 to 0.001nM and the ratio of the fluorescence emission intensity of the system (F 430/F 505) (R 2=0.9901), and its calculated detection limit is 3.76×10-9 n M. In addition, the CD/Cu-MOFs ratio fluorescence sensor has achieved a good recovery rate of standard addition in the actual food sample recovery experiment, which provides an effective method for the detection of H g 2+ in food samples.

Ultrasensitive and Reliable SERS Chip Based on Facile Assembly of AgNPs on Porous LIG to Enhance the Local Electromagnetic Field

Low-concentration molecular detection is of great value in chemical analysis, environmental monitoring, biological analysis, and other trace detection fields. Surface-enhanced Raman scattering (SERS) is widely used in the analysis of low-concentration molecules with great potential for biological detection due to nondestructive measurement. However, detection uniformity and repeatability are challenges in the application of SERS, especially as regards ultrasensitive detection. Here, a AgNPs@LIG SERS chip with excellent sensitivity and uniformity was fabricated by electroplating Ag nanoparticles (AgNPs) on a laser-induced graphene (LIG) surface prepared on a polyimide (PI) film, which realized large-scale production with controllable shape and area. Such an SERS chip features a limit of detection (LOD) of 10–14 M, an enhancement factor (EF) of 3 × 1010, and fine uniformity (∼9.6% relative standard deviation) for rhodamine 6G, benefiting from excellent local electromagnetic field enhancement generated by the gap of AgNPs and excellent performance of porous LIG. Finally, the chip was applied to the detection of melamine with the LOD of 10–9 M, which confirmed the potential application value of the SERS chip for pollutant analysis. In addition, the preparation of the composite SERS chip is simple for mass production, which provides great potential for the development of ultrasensitive SERS biosensors for various biological and chemical analyses.

Thiol stabilized Au nanoclusters with efficient electrochemiluminescence for the simultaneous and ultrasensitive detection of GSH and Cu2+

Herein, an electrochemiluminescence (ECL) biosensor was constructed for simultaneous and ultrasensitive detection of glutathione (GSH) and copper ion (Cu2+) due to thiol (captopril) stabilized gold nanoclusters (Au NCs) as a high-efficient ECL emitter. Impressively, we firstly demonstrated that thiol stabilized Au NCs (thiol-Au NCs) presented unexceptionable ECL performance over amino stabilized Au NCs (amino-Au NCs), due to fast electron transfer from massive Au-S electronic pathways in electrochemical excitation. Furthermore, GSH (target 1) and Cu2+ (target 2) could give rise to “on-off-on” ECL responses of Au NCs based on GSH-triggered competing reaction and Cu2+-specific-DNAzyme walker. As a result, the ECL biosensor achieved trace detection of GSH with a detection limit of 148 pM and Cu2+ with a detection limit of 91.5 fM. Thus, the strategy pointed out a definite direction to obtain ultra-bright ECL metal NCs for multiple biomarker testing, broadening the application in clinical diagnosis.