Sensing Glucose in Urine and Serum and Hydrogen Peroxide in Living Cells by Use of a Novel Boronate Nanoprobe Based on Surface-Enhanced Raman Spectroscopy

Aptamer-controlled gold nanozyme sensor for fluorescent and colorimetric dual-channel detection of methamphetamine

Methamphetamine (METH) is the second abused drug which affects abusers' health and induces social crimes, developing novel methods with high sensitivity and selectivity for METH detecting is still challenging. In this paper, a colorimetric and fluorescent dual-channel sensor for METH has been constructed. We combine the enzyme-mimic catalytic activity of gold nanoparticles (GNPs) with high target specificity of METH aptamer to create a nanosensor (Apt-GNP), in the presence of METH, the absorption of 3,3',5,5'-tetramethylbenzidine (OxTMB) at 650 nm enhanced with METH concentration increasing, while the absorption characteristic peak of GNPs at 530 nm remained almost unchanged. The ratio of A650nm/A530nm and METH concentration had a good linear relationship when METH concentration was in the range of 5-50 μM, and the corresponding linear equation is A650nm/A530nm = 0.00727CMETH (μM) + 0.783 with R2 = 0.997 and LOD = 0.40 μM (LOD = 3σ/s, n = 11). Interestingly, the fluorescence emission of Rhodamine B (RB) overlaps with the absorption spectrum of OxTMB which represents the content of METH and the fluorescence signal of RB can be quenched through internal filtering effect (IEF). Hence, when RB was doped to the detection system, the decay of RB fluorescence can reflect the concentrations change of METH. Accordingly, the linear equation is F/FR = -0.00751CMETH (μM) + 0.895 with R2 = 0.993 and LOD = 0.40 μM, where F was the fluorescence of the analytical solution at 580 nm with METH and FR was fluorescence of RB control solution. The dual-channel sensor can measure METH in serum and artificial urine successfully which is potential to be applied in drug-using crime sites and provide direct evidence to law enforcement officials.

Quantitative Factors Introduced in the Feasibility Analysis of Reactive Oxygen Species (ROS)-Sensitive Triggers

Reactive oxygen species (ROS) are critical for cellular signaling. Various pathophysiological conditions are also associated with elevated levels of ROS. Hence, ROS-sensitive triggers have been extensively used for selective payload delivery. Such applications are predicated on two key functions: (1) a sufficient magnitude of concentration difference for the interested ROS between normal tissue/cells and intended sites and (2) appropriate reaction kinetics to ensure a sufficient level of selectivity for payload release. Further, ROS refers to a group of species with varying reactivity, which should not be viewed as a uniform group. In this review, we critically analyze data on the concentrations of different ROS species under various pathophysiological conditions and examine how reaction kinetics affect the success of ROS-sensitive linker chemistry. Further, we discuss different ROS linker chemistry in the context of their applications in drug delivery and imaging. This review brings new insights into research in ROS-triggered delivery, highlights factors to consider in maximizing the chance for success and discusses pitfalls to avoid.

In situ SERS imaging of protein-specific glycan oxidation on living cells to quantitatively visualize pathogen-cell interactions

Glycan oxidation on the cell surface occurs in many specific life processes including pathogen-cell interactions. This work develops a surface-enhanced Raman scattering (SERS) imaging strategy for in situ quantitative monitoring of protein-specific glycan oxidation mediated pathogen-cell interactions by utilizing Raman reporter DTNB and aptamer co-assembled platinum shelled gold nanoparticles (Au@Pt-DTNB/Apt). Using Fusarium graminearum (FG) and MCF-7 cells as models, Au@Pt-DTNB/Apt can specifically bind to MUC1 protein on the cell surface containing heavy galactose (Gal) and N-acetylgalactosamine (GalNAc) modification. When FG interacts with cells, the secreted galactose oxidase (GO) can oxidize Gal/GalNAc, and the generated reactive oxygen species (ROS) further oxidizes DTNB to produce TNB for greatly enhancing the SERS signal. This strategy can quantitatively visualize for the first time both the protein-specific glycan oxidation and the mediated pathogen-cell interactions, thus providing key quantitative information to distinguish and explore the pathogen-resistance and pharmacological mechanisms of different drugs.

Clinical validation of electrochemical biosensor for the detection of methylglyoxal in subjects with type-2 diabetes mellitus

Methylglyoxal (MG), a highly reactive by-product of glycolysis, is involved in the formation of advanced glycation end-products (AGEs). Elevated levels of MG have been correlated with micro-and macro-angiopathic complications in diabetes, including neuropathy, kidney disease, retinopathy, and cardiovascular disease. Therefore, point-of-care devices for detecting MG may be of great use in the screening of diabetes complications. This study was designed to determine the utility of the developed electrochemical biosensor to measure the level of MG in human plasma from type-2 diabetes mellitus patients. Electrochemical studies were carried out with optimized experimental parameters using the modified Platinum-electrode. Subsequently, clinical studies using 350 blood plasma samples were conducted and the results were validated against the ELISA kit, Normal Glucose Tolerance (NGT), and glycosylated haemoglobin (HbA1c). The MG sensor exhibited a linear range of 1.0-7.5 μM concentration with a sensitivity of 1.02 mA µM-1, a limit of detection of 0.21 µM, a limit of quantification of 0.70 µM and a response time less than 10 s. The sensor showed 90% correlation with ELISA data. The developed biosensor showed a significant correlation with HbA1c and fasting plasma glucose suggesting that it can be used as a point-of-care device to screen for diabetes.

Determination of H2O2 and its antioxidant activity by BCM@Au NPs ratiometric SERS sensor

As a reactive oxygen species (ROS), excessive production of H2O2 contributes to the development of several diseases such as, inflammation, cancer, and respiratory diseases. Supplementation with endogenous or exogenous antioxidants can scavenge ROS and reduce the oxidation of cellular molecules, thus alleviating the generation of diseases. Therefore, the determination of H2O2 content and its antioxidant activity is of great importance in disease diagnosis and treatment. In this paper, a ratiometric SERS sensor with a flexible cellulose membrane was designed for quantitative detection of H2O2 and assessment of antioxidant activity. First, gold seeds were reduced on bacterial cellulose membrane (BCM) and Au NPs were smoothly deposited on the bacterial cellulose membrane (BCM) using halides to reduce the reduction potential in the growth solution to form a flexible BCM@Au NPs SERS substrate. Afterwards, the oxidation of H2O2 was used to convert 3-mercaptophenylboronic acid (3-MPBA) to the corresponding phenol form 3-hydroxyphenylethanol (3-HTP). The change of substance resulted in a good linear relationship between the intensity ratio corresponding to the two Raman shifts of 881 cm-1 and 995 cm-1 and the H2O2 concentration with a detection limit of 0.0186 μM. This opens up a new method for the detection of H2O2 with high sensitivity and accuracy. In addition, this SERS platform was successfully used for the determination of antioxidant activity. It is promising to be applied to disease diagnosis and efficacy evaluation.

A ratiometric SERS sensor with one signal probe for ultrasensitive and quantitative monitoring of serum xanthine

Xanthine can be converted into uric acid, and a high concentration of xanthine in the human body can cause many diseases. Therefore, it is important to develop a sensitive, simple, and reliable approach for measuring xanthine in biological liquids. Hence, a ratiometric surface-enhanced Raman spectroscopy (SERS) sensing strategy with one signal probe was exploited for reliable, sensitive, and quantitative monitoring of serum xanthine. 3-Mercaptophenylboronic acid (3-MPBA) was used as a typical reference with a Raman peak at 996 cm-1. First, 3-MPBA was bound to gold nanoflowers@silica (GNFs@Si) through Au-S bonds. Xanthine oxidase (XOD) catalyzed the oxidation of xanthine into H2O2 on GNFs@Si. Afterward, the obtained H2O2 further reduced 3-MPBA to 3-hydroxythiophenol (3-HTP) accompanied by the emergence of a new Raman peak at 883 cm-1. Meanwhile, the Raman intensity at 996 cm-1 remained constant. Therefore, the ratio of I883/I996 increased with the increasing of xanthine concentration, thus realizing quantitative detection of xanthine. As a result, a ratiometric SERS sensor for the detection of xanthine was proposed with a detection limit of 5.7 nM for xanthine. The novel ratiometric SERS sensor provides a new direction for analyzing other biomolecules with high sensitivity and reliability.

Glucose sandwich assay based on surface-enhanced Raman spectroscopy

A facile and sensitive glucose sandwich assay using surface-enhanced Raman scattering (SERS) has been developed. Glucose was captured by 3-aminopheyonyl boronic acid (APBA) modified Ag nanoparticles decorated onto a polyamide surface. Then, Ag nanoparticles modified with 3-amino-6-ethynylpicolinonitrile (AEPO) and APBA were used as SERS tags. APBA forms specific cis-diol compounds with glucose molecules avoiding interference by other saccharides and biomolecules in urine enabling its selective detection. As the actual Raman reporter, AEPO exhibited a distinctive SERS peak in the Raman silent region, thus increasing the sensitivity of the glucose detection to 10-11 M. Additionally, the developed SERS assay was reusable, and its applicability in artificial urine samples demonstrated future clinical utility confirming the potential of this innovative technology as a diagnostic tool for glucose sensing.

Research Progress of SERS Sensors Based on Hydrogen Peroxide and Related Substances

Hydrogen peroxide (H2O2) has an important role in living organisms, and its detection is of great importance in medical, chemical, and food safety applications. This review provides a comparison of different types of Surface-enhanced Raman scattering (SERS) sensors for H2O2 and related substances with respect to their detection limits, which are of interest due to high sensitivity compared to conventional sensors. According to the latest research report, this review focuses on the sensing mechanism of different sensors and summarizes the linear range, detection limits, and cellular applications of new SERS sensors, and discusses the limitations in vivo and future prospects of SERS technology for the detection of H2O2.

Surface-Enhanced Raman Scattering Enantioselective Detection of Gastric Cancer-Related d-Amino Acids in Saliva Based on Enzyme-Mediated Cascade Reaction

The unusual d-amino acids (d-AAs), as the counter enantiomer of usual l-amino acids (l-AAs), have evoked increasing attention because of their potential relevance with diseases. Accordingly, it is essential to establish sensitive and selective detection methods for d-AAs without the interferences from l-AAs. The surface-enhanced Raman scattering (SERS) technique is efficacious for the detection of molecules but routinely ineffective in enantiomeric differentiation. d-Proline (d-Pro) and d-alanine (d-Ala) are regarded as biomarkers of gastric cancer. Herein, Raman-active boronate modified SERS chips are constructed to develop a d-amino acid oxidase (DAAO)-mediated cascade reaction-based SERS enantioselective assay for d-Pro and d-Ala. The principle is that DAAO selectively catalyzes the deamination of d-Pro and d-Ala, and the produced H2O2 oxidizes boronate to present a new SERS peak at 883 cm-1 for quantitative analysis in a ratiometric way. A linear range from 20 to 400 μmol/L and a limit of detection down to 14.8 μmol/L are reached. In addition, interferences from l-AAs and many other possible species coexisting in biofluids with the detection of d-Pro and d-Ala are ignorable. Enzyme-mediated cascade reaction-based SERS chips are further utilized for saliva sample analysis, and the total levels of d-Pro and d-Ala in salivary samples from gastric cancer patients are much higher than those of healthy persons. This work provides a solution for SERS enantioselective analysis and noninvasive screening chiral biomolecules for disease diagnosis.

Single-Cell Analysis and Classification according to Multiplexed Proteins via Microdroplet-Based Self-Driven Magnetic Surface-Enhanced Raman Spectroscopy Platforms Assisted with Machine Learning Algorithms

A microdroplet-based surface-enhanced Raman spectroscopy (microdroplet SERS) platform was constructed to envelop individual cells in microdroplets, followed by the SERS detection of their extracellular vesicle-proteins (EV-proteins) via the in-drop immunoassays by use of immunomagnetic beads (iMBs) and immuno-SERS tags (iSERS tags). A unique phenomenon is found that iMBs can start a spontaneous reorientation on the probed cell surface based on the electrostatic force-driven interfacial aggregation effect, which leads EV-proteins and iSERS tags to be gathered from a liquid phase to a cell membrane interface and significantly improves SERS sensitivity to the single-cell analysis level due to the formation of numbers of SERS hotspots. Three EV-proteins from two breast cancer cell lines were collected and further analyzed by machine learning algorithmic tools, which will be helpful for a deeper understanding of breast cancer subtypes from the view of EV-proteins.

Chemical conjugation to differentiate monosaccharides by Raman and surface enhanced Raman spectroscopy

Sugars play important roles in numerous biological processes, from providing energy to modifying proteins to alter their function. Glycosylation, the attachment of a sugar residue to a protein, is the most common post translational modification. Identifying the glycans on a protein is a useful tool both for pharmaceutical development as well as probing the proteome and glycome further. Sugars, however, are difficult analytes to probe due to their isomeric nature. In this work, Raman spectroscopy and surface enhanced Raman spectroscopy (SERS) are used to identify different monosaccharide species based on the vibrational modes of these isomeric analytes. The weak scattering of the sugars was overcome through conjugation with phenylboronic acid to provide a larger Raman scattering cross section and induce slight changes in the observed spectra associated with the structure of the monosaccharides. Spontaneous Raman, SERS in flow, and static SERS detection were performed in order to discriminate between arabinose, fructose, galactose, glucose, mannose, and ribose, as well as provide a method for identification and quantification for these sugar conjugates.

Plasmonic nanorod probes' journey inside plant cells for in vivo SERS sensing and multimodal imaging

Nanoparticle-based platforms are gaining strong interest in plant biology and bioenergy research to monitor and control biological processes in whole plants. However, in vivo monitoring of biomolecules using nanoparticles inside plant cells remains challenging due to the impenetrability of the plant cell wall to nanoparticles beyond the exclusion limits (5-20 nm). To overcome this physical barrier, we have designed unique bimetallic silver-coated gold nanorods (AuNR@Ag) capable of entering plant cells, while conserving key plasmonic properties in the near-infrared (NIR). To demonstrate cellular internalization and tracking of the nanorods inside plant tissue, we used a comprehensive multimodal imaging approach that included transmission electron microscopy (TEM), confocal fluorescence microscopy, two-photon luminescence (TPL), X-ray fluorescence microscopy (XRF), and photoacoustics imaging (PAI). We successfully acquired SERS signals of nanorods in vivo inside plant cells of tobacco leaves. On the same leaf samples, we applied orthogonal imaging methods, TPL and PAI techniques for in vivo imaging of the nanorods. This study first demonstrates the intracellular internalization of AuNR@Ag inside whole plant systems for in vivo SERS analysis in tobacco cells. This work demonstrates the potential of this nanoplatform as a new nanotool for intracellular in vivo biosensing for plant biology.

Real Time and Spatiotemporal Quantification of pH and H2O2 Imbalances with a Multiplex Surface-Enhanced Raman Spectroscopy Nanosensor

Oxidative stress is involved in many aging-related pathological disorders and is the result of defective cellular management of redox reactions. Particularly, hydrogen peroxide (H2O2), is a major byproduct and a common oxidative stress biomarker. Monitoring its dynamics and a direct correlation to diseases remains a challenge due to the complexity of redox reactions. Sensitivity and specificity are major drawbacks for H2O2 sensors regardless of their readout. Luminiscent boronate-based probes such as 3-mercaptophenylboronic acid (3-MPBA) are emerging as the most effective quantitation tool due to their specificity and sensitivity. Problems associated with these probes are limited intracellular sensing, water solubility, selectivity, and quenching. We have synthesized a boronate-based nanosensor with a surface-enhanced Raman spectroscopy (SERS) readout to solve these challenges. Furthermore, we found out that environmental pH gradients, as found in biological samples, affect the sensitivity of boronate-based sensors. When the sensor is in an alkaline environment, the oxidation of 3-MPBA by H2O2 is more favored than in an acidic environment. This leads to different H2O2 measurements depending on pH. To solve this issue, we synthesized a multiplex nanosensor capable of concomitantly quantifying pH and H2O2. Our nanosensor first measures the local pH and based on this value, provides the amount of H2O2. It seems that this pH-dependent sensitivity effect applies to all boronic acid based probes. We tested the multiplexing ability by quantitatively measuring intra- and extracellular pH and H2O2 dynamics under physiological and pathological conditions on healthy cells and cells in which H+ and/or H2O2 homeostasis has been altered.

Design and Synthesis of SERS Materials for In Vivo Molecular Imaging and Biosensing

Surface-enhanced Raman scattering (SERS) is a feasible and ultra-sensitive method for biomedical imaging and disease diagnosis. SERS is widely applied to in vivo imaging due to the development of functional nanoparticles encoded by Raman active molecules (SERS nanoprobes) and improvements in instruments. Herein, the recent developments in SERS active materials and their in vivo imaging and biosensing applications are overviewed. Various SERS substrates that have been successfully used for in vivo imaging are described. Then, the applications of SERS imaging in cancer detection and in vivo intraoperative guidance are summarized. The role of highly sensitive SERS biosensors in guiding the detection and prevention of diseases is discussed in detail. Moreover, its role in the identification and resection of microtumors and as a diagnostic and therapeutic platform is also reviewed. Finally, the progress and challenges associated with SERS active materials, equipment, and clinical translation are described. The present evidence suggests that SERS could be applied in clinical practice in the future.

Skin Interstitial Fluid-Based SERS Tags Labeled Microneedles for Tracking of Peritonitis Progression and Treatment Effect

Skin interstitial fluid (ISF)-based microneedle (MN) sensing has recently exhibited wide promise for the minimally invasive and painless diagnosis of diseases. However, it is still a great challenge to diagnose more disease types due to the limited in situ sensing techniques and insufficient ISF biomarker sources. Herein, ISF is employed to pioneer the tracking of acute peritonitis progression via surface-enhanced Raman scattering (SERS) tags labeled MNs patch technique. Densely deposited core-satellite gold nanoparticles and 3-mercaptophenylboronic acid as a Raman reporter enable the developed MNs patch with high sensitivity and selectivity in the determination of H₂O₂, an indicator of peritonitis development. Importantly, the MNs patch not only reliably tracks the different states of peritonitis but also evaluates the efficacy of drugs in the treatment of peritonitis, as evidenced by the altered SERS signal consistent with plasma pro-inflammatory factor (TNF-α) and peritoneum pathological manifestations. Interestingly, the major source of H₂O₂ in ISF of acute peritonitis investigated may not be through conventional blood capillary filtration pathway. This work provides a new route and technique for the early diagnosis of acute peritonitis and the evaluation of drug therapy effects. The developed MNs patch is promising to serve as a universal sensing tool to greatly enrich the variety and prospect of ISF-based disease diagnosis.

A Background-Free SERS Strategy for Sensitive Detection of Hydrogen Peroxide

The accurate and sensitive detection of biomolecules by surface-enhanced Raman spectroscopy (SERS) is possible, but remains challenging due to the interference from biomolecules in complex samples. Herein, a new SERS sensor is developed for background-free detection of hydrogen peroxide (H₂O₂) with an ultralow detection limit (1 × 10^-10 mol/L), using a Raman-silent strategy. The Au microparticles (Au-RSMPs) resembling rose-stones are devised as SERS substrates with a high enhancement effect, and 4-mercaptophenylboronic acid (4-MPBA) is selected as an H₂O₂-responsive Raman reporter. Upon the reaction with H₂O₂, the phenylboronic group of 4-MPBA was converted to a phenol group, which subsequently reacted with 4-diazonium-phenylalkyne (4-DP), an alkyne-carrying molecule via the azo reaction. The formed product exhibits an intense and sharp SERS signal in the Raman-silent region, avoiding interference of impurities and biomolecules. As a proof-of-concept demonstration, we show that this SERS sensor possesses significant merits towards the determination of H₂O₂ in terms of broad linear range, low limit of detection, and high selectivity, showing promise for the quantitative analysis of H₂O₂ in complicated biological samples.

Nanozyme-based colorimetric biosensor with a systemic quantification algorithm for noninvasive glucose monitoring

Diabetes mellitus accompanies an abnormally high glucose level in the bloodstream. Early diagnosis and proper glycemic management of blood glucose are essential to prevent further progression and complications. Biosensor-based colorimetric detection has progressed and shown potential in portable and inexpensive daily assessment of glucose levels because of its simplicity, low-cost, and convenient operation without sophisticated instrumentation. Colorimetric glucose biosensors commonly use natural enzymes that recognize glucose and chromophores that detect enzymatic reaction products. However, many natural enzymes have inherent defects, limiting their extensive application. Recently, nanozyme-based colorimetric detection has drawn attention due to its merits including high sensitivity, stability under strict reaction conditions, flexible structural design with low-cost materials, and adjustable catalytic activities. This review discusses various nanozyme materials, colorimetric analytic methods and mechanisms, recent machine learning based analytic methods, quantification systems, applications and future directions for monitoring and managing diabetes.

Arsenic Prodrug-Mediated Tumor Microenvironment Modulation Platform for Synergetic Glioblastoma Therapy

Glioblastoma (GBM) has a distinct internal environment characterized by high levels of glutathione (GSH) and low oxygen partial pressure, which significantly restrict most drugs' effectiveness. Arsenic-based drugs are emerging candidates for treating solid tumors; however, relatively high doses in solo systems and inconsistent complementary systems severely damage the normal tissues. We proposed a novel covalently conjugated strategy for arsenic-based therapy via arsenic-boronic acid complex formation. The boronic acid was modified on silver (AgL) to capture As^V under an alkaline condition named arsenate plasmonic complex (APC) with a distinct Raman response. The APC can precisely release the captured As^V in lysosomal acidic pH that specifically targets TME to initiate a multimodal therapeutic effect such as GSH depletion and reactive oxygen species generation. In addition, GSH activation leads to subconverted As^V into As^III, which further facilitated glutathione peroxidase (GPx) and superoxide dismutase inhibition, whereas the tumor selective etching of the silver core triggered by endogenous H₂O₂ that can oxidize to generate highly toxic Ag ions produces and supplies O₂ to help the alleviated hypoxia. Both in vitro and in vivo data verify the APC-based chemotherapy paving the way for efficient nanomedicine-enabled boronate affinity-based arsenic chemotherapeutics for on demand site-specific cancer combination treatment of GBM tumors.

Glucose detection through surface-enhanced Raman spectroscopy: A review

Glucose detection is of vital importance to diabetes diagnosis and treatment. Optical approaches in glucose sensing have received much attention in recent years due to the relatively low cost, portable, and mini-invasive or non-invasive potentials. Surface enhanced Raman spectroscopy (SERS) endows the benefits of extremely high sensitivity because of enhanced signals and specificity due to the fingerprint of molecules of interest. However, the direct detection of glucose through SERS was challenging because of poor adsorption of glucose on bare metals and low cross section of glucose. In order to address these challenges, several approaches were proposed and utilized for glucose detection through SERS. This review article mainly focuses on the development of surface enhanced Raman scattering based glucose sensors in recent 10 years. The sensing mechanisms, rational design and sensing properties to glucose are reviewed. Two strategies are summarized as intrinsic sensing and extrinsic sensing. Four general categories for glucose sensing through SERS are discussed including SERS active platform, partition layer functionalized surface, boronic acid based sensors, and enzymatic reaction based biosensors. Finally, the challenges and outlook for SERS based glucose sensors are also presented.

Gold nanoparticle-based optical nanosensors for food and health safety monitoring: recent advances and future perspectives

Modern society has been facing serious health-related problems including food safety, diseases and illness. Hence, it is urgent to develop analysis methods for the detection and control of food contaminants, disease biomarkers and pathogens. As the traditional instrumental methods have several disadvantages, including being time consuming, and having high cost and laborious procedures, optical nanosensors have emerged as promising alternative or complementary approaches to those traditional ones. With the advantages of simple preparation, high surface-to-volume ratio, excellent biocompatibility, and especially, unique optical properties, gold nanoparticles (AuNPs) have been demonstrated as excellent transducers for optical sensing systems. Herein, we provide an overview of the synthesis of AuNPs and their excellent optical properties that are ideal for the development of optical nanosensors based on local surface plasmon resonance (LSPR), colorimetry, fluorescence resonance energy transfer (FRET), and surface-enhanced Raman scattering (SERS) phenomena. We also review the sensing strategies and their mechanisms, as well as summarizing the recent advances in the monitoring of food contaminants, disease biomarkers and pathogens using developed AuNP-based optical nanosensors in the past seven years (2015-now). Furthermore, trends and challenges in the application of these nanosensors in the determination of those analytes are discussed to suggest possible directions for future developments.

Hydrophilic modification of PVDF-based SERS imprinted membrane for the selective detection of L-tyrosine

The polyvinylidene difluoride (PVDF) membrane has received considerable attention as a flexible surface enhanced Raman scattering (SERS) substrate due to its excellent mechanical and physicochemical properties. However, the poor fouling resistance of PVDF membrane due to its intrinsic hydrophobic property limits its practical application. To address this, in this investigation, a SERS imprinted membrane is synthesized based on W₁₈O₄₉/Ag composites. Firstly, to promote hydrophilicity, N-vinyl-2-pyrrolidone (NVP) and triethoxyvinylsilane (VTES) are copolymerized by hydrolysis condensation and linked with engineered polyvinypyrrolidone (PVP) chains exposed on the surface of membrane. Furthermore, W₁₈O₄₉/Ag composites are dispersed on the membrane under the assistance of polydopamine (pDA) to promote the pollution resistance. Subsequently, in order to demonstrate the practical detection property, W₁₈O₄₉/Ag/PVDF membrane is selected as the SERS substrate to synthesize SERS imprinted membrane by precipitation polymerization for the selective detection of L-tyrosine. The characteristic results reveal that the SERS-imprinted membrane exhibits satisfactory hydrophilicity, and it can effectively degrade the pollutant molecules absorbed on its surface under ultraviolet light illumination. It is proved from the detection results that the LOD of WADP-MIMs for L-tyrosine reached 10^-9 mol L^-1 when the concentration of L-tyrosine changed between 10^-3-10^-9 mol L^-1. The correlation coefficient (R²) is 0.994 and the limit of detection is 10^-9 mol L^-1. Meanwhile, it can be applied for the selective detection of L-tyrosine in mixture samples. Overall, this study presents a novel approach for the hydrophilic modification and pollution resistance enhancement of PVDF-based SERS imprinted membrane, which can be effectively utilized for the selective detection of practical samples.

Portable and Intelligent Urine Glucose Analyzer Based on a CdTe QDs@GOx Aerogel Circular Array Sensor

Diabetes is a public health problem characterized by hyperglycemia, high mortality, and morbidity. A simple, rapid, and sensitive glucose detection method for diabetes screening and health self-management of patients with diabetes is of great significance. Therefore, an attractive urine glucose (UG) analyzer with advantages of fastness, sensitivity, and portability was developed. A cadmium telluride quantum dots (CdTe QDs)@glucose oxidase (GOx) aerogel circular array sensor can emit visible red fluorescence when excited by a 365 nm ultraviolet light source inside the analyzer. When urine samples containing glucose were dropped onto the sensor, glucose was oxidized by GOx to produce hydrogen peroxide (H₂O₂), which quenched the red fluorescence of CdTe QDs. The fluorescence images of the sensor were obtained using a CCD camera, and the linear relationship between the glucose concentration and the gray value of the fluorescence image was established. The analyzer shows good sensitivity (LOD, 0.12 mM) with a wide linear range of 0.12-26 mM. Based on the linear relation, the software of the analyzer was written in the C++ language, which can automatically give the gray value of the image and the corresponding glucose concentration. The UG analyzer was used for the detection of a large number clinical samples and compared with a variety of UG test papers, which all showed good detection performance. The novel analyzer we proposed has an important significance in the screening of diabetes and the self-management of diabetic patients.

First-Row d-Block Element-Catalyzed Carbon-Boron Bond Formation and Related Processes

Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon-boron bond into a carbon-X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row d-block transition metals have become increasingly widely used as catalysts for the formation of a carbon-boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon-boron bonds.

Glucose Detection of 4-Mercaptophenylboronic Acid-Immobilized Gold-Silver Core-Shell Assembled Silica Nanostructure by Surface Enhanced Raman Scattering

The importance of glucose in many biological processes continues to garner increasing research interest in the design and development of efficient biotechnology for the sensitive and selective monitoring of glucose. Here we report on a surface-enhanced Raman scattering (SERS) detection of 4-mercaptophenyl boronic acid (4-MPBA)-immobilized gold-silver core-shell assembled silica nanostructure (SiO₂@Au@Ag@4-MPBA) for quantitative, selective detection of glucose in physiologically relevant concentration. This work confirmed that 4-MPBA converted to 4-mercaptophenol (4-MPhOH) in the presence of H₂O₂. In addition, a calibration curve for H₂O₂ detection of 0.3 µg/mL was successfully detected in the range of 1.0 to 1000 µg/mL. Moreover, the SiO₂@Au@Ag@4-MPBA for glucose detection was developed in the presence of glucose oxidase (GOx) at the optimized condition of 100 µg/mL GOx with 1-h incubation time using 20 µg/mL SiO₂@Au@Ag@4-MPBA and measuring Raman signal at 67 µg/mL SiO₂@Au@Ag. At the optimized condition, the calibration curve in the range of 0.5 to 8.0 mM was successfully developed with an LOD of 0.15 mM. Based on those strategies, the SERS detection of glucose can be achieved in the physiologically relevant concentration range and opened a great promise to develop a SERS-based biosensor for a variety of biomedicine applications.

Electrochemically renewable SERS sensor: A new platform for the detection of metabolites involved in peroxide production

The accurate detection of hydrogen peroxide (H₂O₂)-involved metabolites plays a significant role in the early diagnosis of metabolism-associated diseases, whereas most of current metabolite-sensing systems are often hindered by low sensitivity, interference of coexisting species, or tedious preparation. Herein, an electrochemistry-regenerated surface-enhanced Raman scattering (SERS) sensor was developed to serve as a universal platform for detecting H₂O₂-involved metabolites. The SERS sensor was constructed by modifying newly synthesized 2-mercaptohydroquinone (2-MHQ) molecules on the surface of gold nanoparticles (AuNPs) that were electrochemically predeposited on an ITO electrode. Metabolites were detected through the changes in the SERS spectrum as a result of the reaction of 2-MHQ with H₂O₂ induced by the metabolites. Combining the superiority of SERS fingerprint identification and the specificity of the related enzymatic reactions producing H₂O₂, the designed SERS sensor was highly selective in detecting glucose and uric acid as models of H₂O₂-involved metabolite with limits of detection (LODs) of 0.159 μM and 0.0857 μM, respectively. Moreover, the sensor maintained a high SERS activity even after more than 10 electrochemical regenerations within 2 min, demonstrating its effectiveness for the rapid detection of various metabolites with electrochemistry-driven regulation. Importantly, the presented SERS sensor showed considerable practicability for the detection of metabolites in real serum samples. Accordingly, the SERS sensor is a new detection platform for H₂O₂-involved metabolites detection in biological fluids, which may aid the early diagnosis of metabolism-related diseases.

Fiber Optic Sensors: A Review for Glucose Measurement

Diabetes mellitus is a chronic metabolic disorder, being globally one of the most deadly diseases. This disease requires continually monitoring of the body's glucose levels. There are different types of sensors for measuring glucose, most of them invasive to the patient. Fiber optic sensors have been proven to have advantages compared to conventional sensors and they have great potential for various applications, especially in the biomedical area. Compared to other sensors, they are smaller, easy to handle, mostly non-invasive, thus leading to a lower risk of infection, high precision, well correlated and inexpensive. The objective of this review article is to compare different types of fiber optic sensors made with different experimental techniques applied to biomedicine, especially for glucose sensing. Observations are made on the way of elaboration, as well as the advantages and disadvantages that each one could have in real applications.

Bioapplications of Nanomaterials

Nanobiotechnology is known as the application of nanoscaled techniques in biology which bridges natural science to living organism for improving the quality of life of humans. Nanotechnology was first issued in 1959 and has been rapidly developed, supplying numerous benefits to basic scientific academy and to clinical application including human healthcare, specifically in cancer therapy. This chapter discusses recent advances and potentials of nanotechnology in pharmaceutics, therapeutics, biosensing, bioimaging, and gene delivery that demonstrate the multifunctionality of nanotechnology.

In Situ Growth of AuNPs on Glass Nanofibers for SERS Sensors

It is challenging to fabricate plasmonic nanosensors on high-curvature surfaces with high sensitivity and reproducibility at low cost. Here, we report a facile and straightforward strategy, based on an in situ growth technique, for fabricating glass nanofibers covered by asymmetric gold nanoparticles (AuNPs) with tunable morphologies and adjustable spacings, leading to much improved surface-enhanced Raman scattering (SERS) sensitivity because of hotspots generated by the AuNP surface irregularities and adjacent AuNP coupling. First, nanosensors covered with uniform and well-dispersed citrate-capped spherical AuNPs were constructed using a polystyrene-b-poly(4-vinylpyridine) (PS-P4VP, with 33 mol % P4VP content and 61 kg/mol total molecular weight) block copolymer brush-layer templating method, and then, the deposited AuNPs were grown to asymmetric AuNPs. AuNP morphologies and hence the optical characteristics of AuNP-covered glass nanofibers were easily controlled by the choice of experimental parameters, such as the growth time and growth solution composition. In particular, tunable AuNP average diameters between about 40 and 80 nm with AuNP spacings between about 50 and 1 nm were achieved within 15 min of growth. The SERS sensitivity of branched AuNP-covered nanofibers (3 min growth time) was demonstrated to be more than threefold more intense than that of the original spherical AuNP-covered nanofibers using a 633 nm laser. Finite-difference time-domain simulations were performed, showing that the electric field enhancement is highest for intermediate AuNP diameters. Furthermore, SERS applications of these nanosensors for H₂O₂ detection and pH sensing were demonstrated, offering appealing and promising candidates for real-time monitoring of extra/intracellular species in vitro and in vivo.

An accurate and ultrasensitive SERS sensor with Au-Se interface for bioimaging and in situ quantitation

We propose a stable and highly sensitive Au-Se SERS nanoprobe for bioimaging and in situ quantitation, which aims to break through the limitations of traditional Au-S SERS nanoprobes, such as interference from biothiols and unsatisfactory SERS efficiency.

Raman spectroscopy and neuroscience: from fundamental understanding to disease diagnostics and imaging

Neuroscience would directly benefit from more effective detection techniques, leading to earlier diagnosis of disease. The specificity of Raman spectroscopy is unparalleled, given that a molecular fingerprint is attained for each species. It also allows for label-free detection with relatively inexpensive instrumentation, minimal sample preparation, and rapid sample analysis. This review summarizes Raman spectroscopy-based techniques that have been used to advance the field of neuroscience in recent years.

A Biomimetic Plasmonic Nanoreactor for Reliable Metabolite Detection

Reliable monitoring of metabolites in biofluids is critical for diagnosis, treatment, and long-term management of various diseases. Although widely used, existing enzymatic metabolite assays face challenges in clinical practice primarily due to the susceptibility of enzyme activity to external conditions and the low sensitivity of sensing strategies. Inspired by the micro/nanoscale confined catalytic environment in living cells, the coencapsulation of oxidoreductase and metal nanoparticles within the nanopores of macroporous silica foams to fabricate all-in-one bio-nanoreactors is reported herein for use in surface-enhanced Raman scattering (SERS)-based metabolic assays. The enhancement of catalytical activity and stability of enzyme against high temperatures, long-time storage or proteolytic agents are demonstrated. The nanoreactors recognize and catalyze oxidation of the metabolite, and provide ratiometric SERS response in the presence of the enzymatic by-product H2O2, enabling sensitive metabolite quantification in a "sample in and answer out" manner. The nanoreactor makes any oxidoreductase-responsible metabolite a candidate for quantitative SERS sensing, as shown for glucose and lactate. Glucose levels of patients with bacterial infection are accurately analyzed with only 20 µL of cerebrospinal fluids, indicating the potential application of the nanoreactor in vitro clinical testing.

Novel Platinum-Porphyrin as Sensing Compound for Efficient Fluorescent and Electrochemical Detection of H2O2

Metalloporphyrins are highly recognized for their capacity to act as sensitive substances used in formulation of optical, fluorescent, and electrochemical sensors. A novel compound, namely Pt(II)-5,10,15,20-tetra-(4-allyloxy-phenyl) porphyrin, was synthesized by metalation with PtCl2(PhCN)2 of the corresponding porphyrin base and was fully characterized by UV-vis, fluorimetry, FT-IR, 1H-NMR, and 13C-NMR methods. The fluorescence response of this Pt-porphyrin in the presence of different concentrations of hydrogen peroxide was investigated. Besides, modified glassy carbon electrodes with this Pt-porphyrin (Pt-Porf-GCE) were realized and several electrochemical characterizations were comparatively performed with bare glassy carbon electrodes (GCE), in the absence or presence of hydrogen peroxide. The Pt-porphyrin demonstrated to be a successful sensitive material for the detection of hydrogen peroxide both by fluorimetric method in a concentration range relevant for biological samples (1.05–3.9 × 10−7 M) and by electrochemical method, in a larger concentration range from 1 × 10−6 M to 5 × 10−5 M. Based on different methods, this Pt-porphyrin can cover detection in diverse fields, from medical tests to food and agricultural monitoring, proving high accuracy (correlation coefficients over 99%) in both fluorimetric and electrochemical measurements.

A Benchtop Method for Appending Protic Functional Groups to N-Heterocyclic Carbene Protected Gold Nanoparticles

The remarkable resilience of N-heterocyclic carbene (NHC) gold bonds has quickly made NHCs the ligand of choice when functionalizing gold surfaces. Despite rapid progress using deposition from free or CO₂ -protected NHCs, synthetic challenges hinder the functionalization of NHC surfaces with protic functional groups, such as alcohols and amines, particularly on larger nanoparticles. Here, we synthesize NHC-functionalized gold surfaces from gold(I) NHC complexes and aqueous nanoparticles without the need for additional reagents, enabling otherwise difficult functional groups to be appended to the carbene. The resilience of the NHC-Au bond allows for multi-step post-synthetic modification. Beginning with the nitro-NHC, we form an amine-NHC terminated surface, which further undergoes amide coupling with carboxylic acids. The simplicity of this approach, its compatibility with aqueous nanoparticle solutions, and its ability to yield protic functionality, greatly expands the potential of NHC-functionalized noble metal surfaces.

Fabrication of the Ni/ZnO/BiOI foam for the improved electrochemical biosensing performance to glucose

The Ni foam decorated with ZnO/BiOI core-shell p-n junction nanorods was prepared and employed as an enzyme loading matrix to detect glucose. The detection potential was decreased significantly (0.3 V) and the sensitivity was enhanced largely (115.2 μA mM^-1 cm^-2). The metal-semiconductor foam can afford the porous surface for loading enzymes and achieving the multiple catalysis. More important, the built-in electric field and electron well in the p-n junction interface provide the driving force for electron transport. It was an effective strategy to enhance the biosensing performance by the rational design of p-n junction.

A simple enzyme-free SERS sensor for the rapid and sensitive detection of hydrogen peroxide in food

A simple enzyme-free method based on surface-enhanced Raman scattering (SERS) was developed for the first time to detect H₂O₂ in food by etching a self-assembled film of silver nanoparticles (Ag NPs) on a glass substrate.

Detection of humic acid in water using flat-sheet and folded-rod viscous alkaline glucose syrups

Interaction of the alkaline glucose solution with humic acid.

A review on recent advances in the applications of surface-enhanced Raman scattering in analytical chemistry

This review is focused on recent developments of surface-enhanced Raman scattering (SERS) applications in Analytical Chemistry. The work covers advances in the fabrication methods of SERS substrates, including nanoparticles immobilization techniques and advanced nanopatterning with metallic features. Recent insights in quantitative and sampling methods for SERS implementation and the development of new SERS-based approaches for both qualitative and quantitative analysis are discussed. The advent of methods for pre-concentration and new approaches for single-molecule SERS quantification, such as the digital SERS procedure, has provided additional improvements in the analytical figures-of-merit for analysis and assays based on SERS. The use of metal nanostructures as SERS detection elements integrated in devices, such as microfluidic systems and optical fibers, provided new tools for SERS applications that expand beyond the laboratory environment, bringing new opportunities for real-time field tests and process monitoring based on SERS. Finally, selected examples of SERS applications in analytical and bioanalytical chemistry are discussed. The breadth of this work reflects the vast diversity of subjects and approaches that are inherent to the SERS field. The state of the field indicates the potential for a variety of new SERS-based methods and technologies that can be routinely applied in analytical laboratories.

Intracellular and Cellular Detection by SERS-Active Plasmonic Nanostructures

Surface-enhanced Raman scattering (SERS), with greatly amplified fingerprint spectra, holds great promise in biochemical and biomedical research. In particular, the possibility of exciting a library of SERS probes and differentially detecting them simultaneously has stimulated widespread interest in multiplexed biodetection. Herein, recent progress in developing SERS-active plasmonic nanostructures for cellular and intracellular detection is summarized. The development of nanosensors with tailored plasmonic and multifunctional properties for profiling molecular and pathological processes is highlighted. Future challenges towards the routine use of SERS technology in quantitative bioanalysis and clinical diagnostics are further discussed.

Aggregation of Gold Nanoparticles Caused in Two Different Ways Involved in 4-Mercaptophenylboronic Acidand Hydrogen Peroxide

The difference in gold nanoparticle (AuNPs) aggregation caused by different mixing orders of AuNPs, 4-mercaptophenylboronic acid (4-MPBA), and hydrogen peroxide (H₂O₂) has been scarcely reported. We have found that the color change of a ((4-MPBA + AuNPs) + H₂O₂) mixture caused by H₂O₂ is more sensitive than that of a ((4-MPBA + H₂O₂) + AuNPs) mixture. For the former mixture, the color changes obviously with H₂O₂ concentrations in the range of 0~0.025%. However, for the latter mixture, the corresponding H₂O₂ concentration is in the range of 0~1.93%. The mechanisms on the color change originating from the aggregation of AuNPs occurring in the two mixtures were investigated in detail. For the ((4-MPBA + H₂O₂) + AuNPs) mixture, free 4-MPBA is oxidized by H₂O₂ to form bis(4-hydroxyphenyl) disulfide (BHPD) and peroxoboric acid. However, for the ((4-MPBA+AuNPs) + H₂O₂) mixture, immobilized 4-MPBA is oxidized by H₂O₂ to form 4-hydroxythiophenol (4-HTP) and boric acid. The decrease in charge on the surface of AuNPs caused by BHPD, which has alarger steric hindrance, is poorer than that caused by -4-HTP, and this is mainly responsible for the difference in the aggregation of AuNPs in the two mixtures. The formation of boric acid and peroxoboric acid in the reaction between 4-MPBA and H₂O₂ can alter the pH of the medium, and the effect of the pH change on the aggregation of AuNPs should not be ignored. These findings not only offer a new strategy in colorimetric assays to expand the detection range of hydrogen peroxide concentrations but also assist in deepening the understanding of the aggregation of citrate-capped AuNPs involved in 4-MPBA and H₂O₂, as well as in developing other probes.