On-Site and Quantitative Detection of Trace Methamphetamine in Urine/Serum Samples with a Surface-Enhanced Raman Scattering-Active Microcavity and Rapid Pretreatment Device

Calixarene-Based Magnetic Nanosponge Decorating AgNPs for Rapid and Selective Surface-Enhanced Raman Scattering Analysis in Complex Samples

Rapid and accurate analysis of trace targets in complex samples remains an enormous challenge. Herein, the calix[x]arene-based magnetic cross-linked polymer decorating AgNPs, abbreviated Fe3O4-CXA-DAB@AgNPs nanosponge, was developed for fast surface-enhanced Raman scattering (SERS) analysis in complex samples. The Fe3O4-CXA-DAB@AgNPs nanosponge surface was constructed by high-density CXA units with special cavity size and structure, which could selectively recognize and enrich targets to the sensing surface by the host-guest effect and molecule interactions. The Fe3O4-C4A-DAB@AgNPs showed significant SERS enhancement to choline chloride (ChCl) and succinylcholine chloride (SCC) with an enhancement factor (EF) of 2.9 × 107 and 6.3 × 106, respectively. The Fe3O4-C6A-DAB@AgNPs exhibited high SERS activity to thiabendazole with an EF of 7.6 × 106. Introducing recognition-enrichment-separation with SERS sensing, the nanosponge could achieve rapid enrichment sensing of targets within 6-8 min. Also, the Fe3O4-CXA-DAB@AgNPs nanosponge exhibited good stability for rapid detection with relative standard deviations less than 6.3% for intra-batch (n = 25) and 6.8% for inter-batch (n = 15). Benefiting from these merits, the Fe3O4-C4A-DAB@AgNPs was employed for fast SERS analysis of ChCl and SCC in real samples. The limits of detection were 0.62 μg/L for ChCl and 2.0 μg/L for SCC. ChCl was found in feed sample with recoveries of 85.3-108%, and SCC was found in serum samples with recoveries of 85.7-111%. The methods provided a significant reference for the selective analysis of targets by regulating the calix[x]arenes cavity size to satisfy different molecules and rapid quantification strategy by integrating sample pretreatment technology with sensing detection all-in-one.

Boronic acid ester-based hydrogel as surface-enhanced Raman scattering substrates for separation, enrichment, hydrolysis and detection of hydrogen peroxide residue in dairy product all-in-one

Rapid and selective separation, enrichment and detection of trace residue all-in-one in complex samples is a major challenge. Hydrogels with molecular sieve properties can selectively separate and enrich target analytes, and the combination with high sensitivity detection of surface-enhanced Raman scattering (SERS) is expected to achieve the above all-in-one detection. Herein, the core-shell structured Au@poly(N-isopropylacrylamide)-phenylboronic acid hydrogel (Au@PNIP-VBA) with boronic acid ester groups was prepared by thermally initiated polymerization. The boronic acid ester groups in hydrogel are selectively hydrolyzed by hydrogen peroxide (H2O2) to hydroxyl structures, leading to a reduction in SERS signals. The Au@PNIP-VBA hydrogel has molecular sieve properties and high SERS activity, making it suitable for separation, enrichment, hydrolysis and detection of H2O2 all-in-one. A rapid SERS method was developed for analysis of H2O2 based on the Au@PNIP-VBA hydrogel with the linear range of 8.5 × 10-2-6.8 mg L-1 and the detection limit of 33 μg L-1. The method was successfully applied to the determination of H2O2 residue in fresh milk, pure milk, yogurt and camel milk, with the recoveries were in the range of 82.2%-109.3% and the relative standard deviations were 2.8%-8.3%. This efficient all-in-one strategy has the advantages of simple sample pre-treatment, rapid analysis (30 min) and high sensitivity, making it highly promising for food quality and safety analysis.

A sensor platform based on SERS detection/janus textile for sweat glucose and lactate analysis toward portable monitoring of wellness status

Herein we report a wearable sweat sensor of a Janus fabric based on surface enhanced Raman scattering (SERS) technology, mainly detecting the two important metabolites glucose and lactate. Janus fabric is composed of electrospinning PU on a piece of medical gauze (cotton), working as the unidirectional moisture transport component (R = 1305%) to collect and transfer sweat efficiently. SERS tags with different structures act as the probe to recognize and detect the glucose and lactate in high sensitivity. Core-shell structured gold nanorods with DTNB inside (AuNRs@DTNB@Au) are used to detect lactate, while gold nanorods with MPBA (AuNRs@MPBA) are used to detect glucose. Through the characteristic SERS information, two calibration functions were established for the concentration determination of glucose and lactate. The concentrations of glucose and lactate in sweat of a 23 years volunteer during three-stage interval running are tested to be 95.5, 53.2, 30.5 μM and 4.9, 13.9, 10.8 mM, indicating the glucose (energy) consumption during exercise and the rapid accumulation of lactate at the early stage accompanied by the subsequent relief. As expected, this sensing system is able to provide a novel strategy for effective acquisition and rapid detection of essential biomarkers in sweat.

From Lab to Life: Self-Powered Sweat Sensors and Their Future in Personal Health Monitoring

The rapid development of wearable sweat sensors has demonstrated their potential for continuous, non-invasive disease diagnosis and health monitoring. Emerging energy harvesters capable of converting various environmental energy sources-biomechanical, thermal, biochemical, and solar-into electrical energy are revolutionizing power solutions for wearable devices. Based on self-powered technology, the integration of the energy harvesters with wearable sweat sensors can drive the device for biosensing, signal processing, and data transmission. As a result, self-powered sweat sensors are able to operate continuously without external power or charging, greatly facilitating the development of wearable electronics and personalized healthcare. This review focuses on the recent advances in self-powered sweat sensors for personalized healthcare, covering sweat sensors, energy harvesters, energy management, and applications. The review begins with the foundations of wearable sweat sensors, providing an overview of their detection methods, materials, and wearable devices. Then, the working mechanism, structure, and a characteristic of different types of energy harvesters are discussed. The features and challenges of different energy harvesters in energy supply and energy management of sweat sensors are emphasized. The review concludes with a look at the future prospects of self-powered sweat sensors, outlining the trajectory of the field and its potential to flourish.

Inkjet Printing Patterned Plasmonic SERS Platform with Surface-Optimized Paper for Label-Free Detection of Illegal Drugs in Urine

Rapid quantitative testing of illegal drugs is urgently needed for precisely cracking down on drug crimes. Herein, an optimized paper-based surface-enhanced Raman spectroscopy (SERS) platform with patterned printing of plasmonic nanoparticles was constructed for the on-site quick testing of illegal drugs in urine. The filter paper was first coated with a layer of positive-charged chitosan, so as to reduce its roughness by filling the holes of the cellulose matrix and enhance the adhesion of negative-charged silver ink. Subsequently, hydrophobic modification was performed based on the binary silylation reaction, which could obviously improve the sensitivity of the paper-based SERS substrate by concentrating the amount of analyte. Meanwhile, SERS-active silver ink was fabricated and further printed on the surface of the above modified paper with custom-designed pattern (3 × 6). The performance of this SERS platform was assessed by using crystal violet (CV) as a model tag, and the obtained results proved it possesses excellent sensitivity and reproducibility, in which the relative standard deviation (RSD) dropped remarkably. More importantly, as a proof of concept, rapid detection of standard methylamphetamine (MAMP), one of the most widely abused drugs, was achieved with a limit of detection (LOD) of 1.43 ppb using a portable Raman spectrometer. And it also had a good capability in human urine sample detection, with a correlation index (R2) up to 0.9927. This optimized paper-based SERS platform was easily manufactured, cheap, and portable, providing a new strategy for the on-site detection of illicit drugs.

Rapid Sample Pretreatment Facilitating SERS Detection of Trace Weak Organic Acids/Bases in Complex Matrices

Fast and efficient sample pretreatment is the prerequisite for realizing surface-enhanced Raman spectroscopy (SERS) detection of trace targets in complex matrices, which is still a big issue for the practical application of SERS. Recently, we have proposed a highly performed liquid-liquid extraction (LLE)-back extraction (BE) for weak acids/bases extraction in drinking water and beverage samples. However, the performance efficiency decreased drastically on facing matrices like food and biological blood. Based on the total interaction energies among target, interferent, and extractant molecules, solid-phase extraction (SPE) with a higher selectivity was introduced in advance of LLE-BE, which enabled the sensitive (μg L-1 level) and rapid (within 10 min) SERS detection of both koumine (a weak base) and celastrol (a weak acid) in different food and biological samples. Further, the high SERS sensitivity was determined unmanned by Vis-CAD (a machine learning algorithm), instead of the highly demanded expert recognition. The generality of SPE-LLE-BE for various weak acids/bases (2 < pKa < 12), accompanied by the high efficiency, easy operation, and low cost, offers SERS as a powerful on-site and efficient inspection tool in food safety and forensics.

Detection and Identification of Pesticides in Fruits Coupling to an Au-Au Nanorod Array SERS Substrate and RF-1D-CNN Model Analysis

In this research, a method was developed for fabricating Au-Au nanorod array substrates through the deposition of large-area Au nanostructures on an Au nanorod array using a galvanic cell reaction. The incorporation of a granular structure enhanced both the number and intensity of surface-enhanced Raman scattering (SERS) hot spots on the substrate, thereby elevating the SERS performance beyond that of substrates composed solely of an Au nanorod. Calculations using the finite difference time domain method confirmed the generation of a strong electromagnetic field around the nanoparticles. Motivated by the electromotive force, Au ions in the chloroauric acid solution were reduced to form nanostructures on the nanorod array. The size and distribution density of these granular nanostructures could be modulated by varying the reaction time and the concentration of chloroauric acid. The resulting Au-Au nanorod array substrate exhibited an active, uniform, and reproducible SERS effect. With 1,2-bis(4-pyridyl)ethylene as the probe molecule, the detection sensitivity of the Au-Au nanorod array substrate was enhanced to 10-11 M, improving by five orders of magnitude over the substrate consisting only of an Au nanorod array. For a practical application, this substrate was utilized for the detection of pesticides, including thiram, thiabendazole, carbendazim, and phosmet, within the concentration range of 10-4 to 5 × 10-7 M. An analytical model combining a random forest and a one-dimensional convolutional neural network, referring to the important variable-one-dimensional convolutional neural network model, was developed for the precise identification of thiram. This approach demonstrated significant potential for biochemical sensing and rapid on-site identification.

A Portable Array Visualization Device Integrating Sample Preparation and Detection All-in-One for the On-Site Analysis of Complex Samples

A gas membrane separation/array fluorescence visualization (GMS/AFV) device is developed by integrating hydrazine-based carbonized copolymer dots (PD-N2H4) for visual on-site analysis. The novel PD-N2H4 was synthesized using a "polymer template" approach, exhibiting strong blue fluorescence capable of visual sensing. The GMS/AFV device integrates sample preparation and detection all-in-one, consisting of a smartphone, a sample pretreatment system, and an optical system. In the detection procedure, the samples will be treated in the sample pretreatment system to create volatile gases. Therefore, any gas samples as well as solid and liquid samples that potentially produce volatile gases can be visually detected on-site by the device. H2S was utilized as a model analyte to test the practicality of the GMS/AFV device. The entire analysis can be finished in 3 min, and the limit of detection of H2S is as low as 3.4 μg/L. Surprisingly, the device is also capable of high-throughput sample detection, which can process 48 samples simultaneously in about 20 min. The device offers a quick, easy, cheap, and environmentally friendly way to analyze volatile gases, and it creates new opportunities for on-site detection of complex samples.

Cobalt oxyhydroxide nanosheet-modulated ratiometric fluorescence platform for the selective detection of malachite green in fish

A ratiometric fluorescence platform was developed based on the cobalt oxyhydroxide (CoOOH) nanosheet-modulated fluorescence response of blue emissive copper nanoclusters (Cu NCs) and yellow emissive o-phenylenediamine (OPD). CoOOH nanosheets showed dual function of strong absorption and oxidation ability, which can effectively quench the blue fluorescence of Cu NCs, with an excitation and emission peak maximum at 390 and 450 nm, respectively , and transfer the OPD into yellow fluorescence products, with an excitation and emission peak maximum at 390 and 560 nm, respectively. Upon introducing butyrylcholinesterase (BChE) and its substrates, CoOOH nanosheets were decomposed into Co2+, and malachite green (MG) showed strong inhibition ability to this  process. This resulted in the obvious difference on the ratio of blue and yellow fluorescence recorded on the system in the presence and absence of MG, which was utilized for the quantitative detection of MG, with a limit of detection of 0.140 μM and a coefficient of variation of 3.5%. The fluorescence ratiometric assay showed excellent detection performances in practical sample analysis.

Fe3O4-carboxyl modified AuNPs-chitosan@AgNPs as a robust surface-enhanced Raman scattering substrate for rapid analysis of tryptamine and ofloxacin in aquatic products

Rapid and accurate quantification of trace targets in complex samples is an extremely challenging issue in fast analysis field. Herein, we developed Fe3O4-carboxyl modified AuNPs-chitosan@AgNPs composite (Fe3O4-AuNCs-Cs@AgNPs) as a robust surface-enhanced Raman scattering (SERS) substrate for rapid analysis of tryptamine (TPA) and ofloxacin (OFX). The substrate possessed abundant surficial active sites of -NH2, -OH and -COOH groups. The substrate exhibited good SERS activity for several different model molecules with enhancement factors (EFs) of 1.2 × 108 for 4-mercaptobenzoic acid. The substrate presented good stability for detection of TPA at pH 6.0 and OFX at pH 8.0, and relative standard deviations less than 5.0% for intra-batch and 6.0% for inter-batch. Also, the substrate possessed good time-stability within 50 days. The substrate integrated advantages of efficient enrichment, fast magnetic separation, and strong localized surface plasmon resonance properties of AgNPs. With versatile merits, TPA and OFX can be enriched and separated within 10 min. SERS methods for analysis of TPA and OFX were developed with detection limits of 35.5 μg/L and 15.8 μg/L, respectively. TPA and OFX were actually found in aquatic product, and recoveries during sample analysis were 89.3%-110% for TPA and 89.3%-96.8% for OFX. The analytical process completed within 30 min via enrichment-separation-detection all-in-one, exhibiting great potential for rapid analysis of toxic biogenic monoamines and antibiotic residues in food.

SERS and machine learning based effective feature extraction for detection and identification of amphetamine analogs

Surface-enhanced Raman spectroscopy (SERS) is extensively researched in diverse disciplines due to its sensitivity and non-destructive nature. It is particularly considered a potential and promising technology for rapid on-site screening in drug detection. In this investigation, a technique was developed for fabricating nanocrystals of Ag@Au SNCs. Ag@Au SNCs, as the basic material of SERS, can detect amphetamine at concentrations as low as 1 μg/mL. The Ag@Au SNCs exhibits a strong surface plasmon resonance effect, which amplifies molecular signals. The SERS spectra of ten substances, including amphetamine and its analogs, showed a strong peak signal. To establish a qualitative distinction, we examined the Raman spectra and conducted density functional theory (DFT) calculations on the ten aforementioned species. The DFT calculation enabled us to determine the vibrational frequency and assign normal modes, thereby facilitating the qualitative differentiation of amphetamines and its analogs. Furthermore, the SERS spectrum of the ten mentioned substances was analysed using the support vector machine learning algorithm, which yielded a discrimination accuracy of 98.0 %.

Rapid and Robust Analysis of Coumatetralyl in Environmental Water and Human Urine Using a Portable Raman Spectrometer

The widespread use and exposure of coumatetralyl (CMTT) has led to its accumulation in the environment and organisms, causing damage to ecosystems and adverse health effects in humans. Unfortunately, achieving fast detection of CMTT remains challenging. Herein, a rapid and robust surface-enhanced Raman spectroscopy (SERS) method was developed for rapid on-site detection of CMTT in environmental water and human urine. Clear trends were observed between the signal intensity and the logarithmic concentration of CMTT, ranging from 0.025 to 5.0 μg/mL with high reproducibility. The detection limits in water and human urine were as low as 1.53 and 13.71 ng/mL, respectively. The recoveries of CMTT for environmental water and urine samples were 90.2-98.2 and 82.0-87.5%, respectively, satisfactory for practical applications. The quantitative results of this approach were highly comparable to those obtained by high-performance liquid chromatography. Most importantly, it is cost-effective, operationally simple, and without a complicated sample preparation step. Detecting CMTT in water samples took only 5 min, and the detection of urine samples was completed within 8 min. This simple yet practical SERS approach offers a reliable application prospect for on-site CMTT detection in environmental water and point-of-care monitoring of poisoned patients.

Au@Ag nanodome-cones array substrate for efficient residue analysis of food samples by surface-enhanced Raman scattering

A bioinspired Au@Ag nanodome-cones array (Au@Ag NDCA) surface-enhanced Raman scattering (SERS) chip was developed for efficient residue analyses of food samples. The cicada wing inspired Au@Ag NDCA chip was fabricated by a bottom-up method, Au nanocones array was firstly grown onto nickel foil by displacement reaction and cetyltrimethylammonium bromide guidance growth, and then silver shell with controllable thickness was coated onto the Au nanocones array by magnetron sputtering. The Au@Ag NDCA chip exhibited good SERS performances with high enhancement factor of 1.2 × 10⁸, good uniformity with relative standard deviation (RSD) less than 7.5% (n = 25), good inter-batch reproducibility with RSD less than 9.4% (n = 9), and long-term stability over 9 weeks. By adapting a minimized sample preparation, Au@Ag NDCA chip combined with a 96-well plate could realize high-throughput SERS analyses of 96 samples with average analysis time less than 10 min. The substrate was applied for quantitative analyses of two food projects. One was 6-benzylaminopurine auxin residue in sprout samples with detection limit of 38.8 μg/L, recoveries of 93.3-105.4% and RSDs of 1.5-6.5%, and the other was an edible spice of 4-amino-5,6-dimethylthieno (2,3-d) pyrimidin-2(1H)-one hydrochloride additive in beverage samples with detection limit of 18.0 μg/L, recoveries of 96.2-106.6% and RSDs of 3.5-7.9%. All the SERS results were well confirmed by conventional high-performance liquid chromatographic methods with relative errors less than 9.7%. The robust Au@Ag NDCA chip exhibited good analytical performances possessed great potential for convenient and reliable analyses of food quality and safety.

Detection of 3,4-Methylene Dioxy Amphetamine in Urine by Magnetically Improved Surface-Enhanced Raman Scattering Sensing Strategy

Abuse of illicit drugs has become a major issue of global concern. As a synthetic amphetamine analog, 3,4-Methylene Dioxy Amphetamine (MDA) causes serotonergic neurotoxicity, posing a serious risk to human health. In this work, a two-dimensional substrate of ITO/Au is fabricated by transferring Au nanoparticle film onto indium–tin oxide glass (ITO). By magnetic inducing assembly of Fe₃O₄@Au onto ITO/Au, a sandwich-based, surface-enhanced Raman scattering (SERS) detection strategy is designed. Through the use of an external magnet, the MDA is retained in the region of hot spots formed between Fe₃O₄@Au and ITO/Au; as a result, the SERS sensitivity for MDA is superior compared to other methods, lowering the limit of detection (LOD) to 0.0685 ng/mL and attaining a corresponding linear dynamic detection range of 5–10⁵ ng/mL. As an actual application, this magnetically improved SERS sensing strategy is successfully applied to distinguish MDA in urine at trace level, which is beneficial to clinical and forensic monitors.

Polydopamine inner wall-coated hypodermic needle as microextraction device and electrospray emitter for the direct analysis of illicit drugs in oral fluid by ambient mass spectrometry

In this article, polydopamine inner wall-coated hypodermic needles (PDA-HNs) are evaluated as both microextraction devices and electrospray ionization (ESI) emitters for determining selected illicit drugs (methamphetamine, cocaine, and methadone) in oral fluid samples. The PDA film, located in the inner wall of the needle, allows the extraction of the analytes at alkaline pH, where their hydrophobic character is promoted. The extracted analytes are finally eluted in a methanol/formic acid mixture that also acts as ESI solution. For this purpose, a dedicated interface based on the connection of a PEEK tube with the needle hub is proposed. This assembly allows delivering the ESI solution by the infusion syringe pump of the mass spectrometer, providing an efficient ESI on the tip of the needle. The double use of the PDA-HNs as microextraction devices and ESI emitters permits the determination of the target analytes with limits of detection and precision (expressed as relative standard deviation) values better than 2.4 μg/L and 17.6%, respectively. The accuracy was evaluated by analyzing independent spiked oral fluid samples, obtaining good results.

Research Progress of Raman Spectroscopy and Raman Imaging in Pharmaceutical Analysis

The analytical investigation of the pharmaceutical process monitors the critical process parameters of the drug, beginning from its development until marketing and postmarketing, and appropriate corrective action can be taken to change the pharmaceutical design at any stage of the process. Advanced analytical methods, such as Raman spectroscopy, are particularly suitable for use in the field of drug analysis, especially for qualitative and quantitative work, due to the advantages of simple sample preparation, fast, nondestructive analysis speed, and effective avoidance of moisture interference. Advanced Raman imaging techniques have gradually become a powerful alternative method for monitoring changes in polymorph distribution and active pharmaceutical ingredient distribution in drug processing and pharmacokinetics. Surface-enhanced Raman spectroscopy (SERS) has also solved the inherent insensitivity and fluorescence problems of Raman, which has made good progress in the field of illegal drug analysis. This review summarizes the application of Raman spectroscopy and imaging technology, which are used in the qualitative and quantitative analysis of solid tablets, quality control of the production process, drug crystal analysis, illegal drug analysis, and monitoring of drug dissolution and release in the field of drug analysis in recent years.

Rapid and Simple Analysis of the Human Pepsin Secondary Structure Using a Portable Raman Spectrometer

Human pepsin is a digestive protease that plays an important role in the human digestive system. The secondary structure of human pepsin determines its bioactivity. Therefore, an in-depth understanding of human pepsin secondary structure changes is particularly important for the further improvement of the efficiency of human pepsin biological function. However, the complexity and diversity of the human pepsin secondary structure make its analysis difficult. Herein, a convenient method has been developed to quickly detect the secondary structure of human pepsin using a portable Raman spectrometer. According to the change of surface-enhanced Raman spectroscopy (SERS) signal intensity and activity of human pepsin at different pH values, we analyze the change of the human pepsin secondary structure. The results show that the content of the β-sheet gradually increased with the increase in the pH in the active range, which is in good agreement with circular dichroism (CD) measurements. The change of the secondary structure improves the sensitivity of human pepsin SERS detection. Meanwhile, human pepsin is a commonly used disease marker for the noninvasive diagnosis of gastroesophageal reflux disease (GERD); the detection limit of human pepsin we obtained is 2 μg/mL by the abovementioned method. The real clinical detection scenario is also simulated by spiking pepsin solution in saliva, and the standard recovery rate is 80.7-92.3%. These results show the great prospect of our method in studying the protein secondary structure and furthermore promote the application of SERS in clinical diagnosis.

Recent advances in developing optical and electrochemical sensors for analysis of methamphetamine: A review

Recognition of misused stimulant drugs has always been a hot topic from a medical and judicial perspective. Methamphetamine (MAMP) is an addictive and illegal drug that profoundly affects the central nervous system. Like other illicit drugs, the detection of MAMP in biological and street samples is vital for several organizations such as forensic medicine, anti-drug headquarters and diagnostic clinics. By emerging nanotechnology and exploiting nanomaterials in sensing applications, a great deal of attention has been given to the design of analytical sensors in MAMP tracing. For the first time, this study has briefly reviewed all the optical and electrochemical sensors in MAMP detection from earlier so far. How various receptors with engineering nanomaterials allow developing novel approaches to measure MAMP have been studied. Fundamental concepts related to optical and electrochemical recognition assays in which nanomaterials have been used and relevant MAMP sensing applications have been comprehensively covered. Challenges, opportunities and future outlooks of this field have also been discussed at the end.

Fabrication of Ag@Au (core@shell) nanorods as a SERS substrate by the oblique angle deposition process and sputtering technology

Gold (Au) and silver (Ag) are the main materials exhibiting strong Surface-Enhanced Raman Scattering (SERS) effects. The Ag nano-rods (AgNRs) and Au nano-rods (AuNRs) SERS substrates prepared using the technology of the oblique angle deposition (OAD) process have received considerable attention in recent years because of their rapid preparation process and good repeatability. However, AgNR substrates are unstable due to the low chemical stability of Ag. To overcome these limitations, an Ag@Au core-shell nano-rod (NR) array SERS substrate was fabricated using the OAD process and sputtering technology. Moreover, simulation analysis was performed using finite-difference time-domain calculations to evaluate the enhancement mechanism of the Ag@Au NR array substrate. Based on the simulation results and actual process conditions, the Ag@Au core-shell NR array substrate with the Au shell thickness of 20 nm was studied. To characterize the substrate's SERS performance, 1,2-bis(4-pyridyl)ethylene (BPE) was used as the Raman probe. The limit of detection of BPE could reach 10-12 M. The Ag@Au NR array substrate demonstrated uniformity with an acceptable relative standard deviation. Despite the strong oxidation of the hydrogen peroxide (H2O2) solution, the Ag@Au NR array substrate maintains good chemical stability and SERS performance. And long-term stability of the Ag@Au NR substrate was observed over 8 months of storage time. Our results show the successful preparation of a highly sensitive, repeatable and stable substrate. Furthermore, this substrate proves great potential in the field of biochemical sensing.

Rapid Formation of Nanoclusters for Detection of Drugs in Urine Using Surface-Enhanced Raman Spectroscopy

We developed a method based on surface-enhanced Raman spectroscopy (SERS) and a sample pretreatment process for rapid, sensitive, reproducible, multiplexed, and low-cost detection of illegal drugs in urine. The abuse of new psychoactive substances (NPS) has become an increasingly serious problem in many countries. However, immunoassay-based screening kits for NPS are usually not available because of the lack of corresponding antibodies. SERS has a great potential for rapid detection of NPS because it can simultaneously detect multiple kinds of drugs without the use of antibodies. To achieve highly sensitive SERS detection of drugs, sodium bromide was first employed to induce the rapid formation of Ag nanoclusters by aggregating silver nanoparticles (AgNPs) in the extracted sample solution. SERS measurements were performed immediately after the sample pretreatment without incubation. The three-dimensional SERS hot spots were believed to form significantly within the nanoclusters, providing strong SERS enhancement effects. The displacement of citrate molecules on the surfaces of the AgNPs by bromide ions helped increase the adsorption of drug molecules, increasing their areal density. We demonstrated the simultaneous detection of two kinds of NPS, methcathinone and 4-methylmethcathinone, in urine at a concentration as low as 0.01 ppm.

Automatic Sensing Setup for Methamphetamine Based on the Reactional Wettability Variation Strategy

An automatic setup for reactional wettability variation (RWV) was developed by interlinking liquid selection and transportation, object movement, and image recognition. In this way, the performance of the RWV strategy is updated to a nearly unmanned control manner with the example of methamphetamine and its aptamer. On the automatic RWV detection setup, the sensing surface acts similarly as before. The aptamer-based sensing surface resulted from the breakdown of the hydrophobic basis. The hydrophobicity is constructed on the metastable aptamer layer, which is responsive to the corresponding target. Methamphetamine interacts with its corresponding aptamer and destroys the basis of the hydrophobicity. A decrease in contact angle indicates the existence of methamphetamine. The RWV phenomenon is also affected by concentration and temperature. The development of an automatic detection ability would bring new possibilities to the surface reaction on smarter detection.