4-mercaptophenylboronic Acid Research Articles

Highly sensitive and selective SERS detection of caspase-3 during cell apoptosis based on the target-induced hotspot effect.

Caspase-3 is an important biomarker for the process of apoptosis, which is a key target for cancer treatment. Due to its low concentration in single cells and the structural similarity of caspase family proteins, it is exceedingly challenging to accurately determine the intracellular caspase-3 during apoptosis in situ. Herein, a biosensing strategy based on the target-induced SERS "hot spot" formation has been developed for the simultaneous highly sensitive and selective detection of intracellular caspase-3 level. The nanosensor is composed of gold nanoparticles modified with the probe molecule 4-mercaptophenylboronic acid (4-MPBA) and a peptide chain. The well-designed peptide chain contains two distinct functional domains, one with a sulfhydryl group for bonding to the gold nanoparticles and the other a fragment specifically recognized by caspase-3. When caspase-3 is present, the negatively charged segment (NH2-Asp-Asp-Asp-Glu-Val-Asp-OH) of the peptide chain is specifically hydrolyzed, leaving a positively charged fragment coated on the surface of the gold nanoparticles. At this time, the golden nanoparticles undergo significant coupling aggregation due to the electrostatic interaction, resulting in a large number of SERS "hot spot" formation. The SERS signal of the 4-MPBA located at the nano-gap is significantly boosted because of the local plasma enhancement effect. The highly sensitive determination of caspase-3 can be achieved according to the altered SERS signal intensity of 4-MPBA. The turn-on of the SERS signal-induced target contributes to the excellent selectivity and the formation of the SERS "hot spot" effect that further improves the sensitivity of caspase-3 detection. The advantages of this biosensing technique allow for the precise in situ monitoring of the dynamic changes in caspase-3 levels during apoptosis. In addition, the differences in caspase-3 levels during the apoptosis of various cell types were compared. Monitoring the caspase-3 levels can be used to track the cellular apoptosis process, evaluate the effect of drugs on cancer cells in real time, and provide guidance for the selection of the appropriate drug dosage.

Surface-Enhanced Raman Scattering in Silver-Coated Suspended-Core Fiber.

In this paper, the silver-coated large-core suspended-core fiber (LSCF) probe was fabricated by the dynamic chemical liquid phase deposition method for surface-enhanced Raman scattering (SERS) sensing. The 4-mercaptophenylboronic acid (4-MPBA) monolayer was assembled in the LSCF as the recognition monolayer. Taking advantage of the appropriate core size of the LSCF, a custom-made Y-type optical fiber patch cable was utilized to connect the semiconductor laser, Raman spectrometer, and the proposed fiber SERS probe. The SERS signal is propagated in the silver-coated air channels, which can effectively reduce the Raman and fluorescence background of the silica core. Experiments were performed to measure the Raman scattering spectra of the 4-MPBA in the silver-coated LSCF in a non-enhanced and enhanced case. The experiment results showed that the Raman signal strength was enhanced more than 6 times by the surface plasmon resonance compared with the non-enhanced case. The proposed LSCF for SERS sensing technology provides huge research value for the fiber SERS probes in biomedicine and environmental science. The combination of SERS and microstructured optical fibers offers a potential approach for SERS detection.

Chemically Tailored Single Atoms for Targeted and Light-Controlled Bactericidal Activity.

Single-atom (SA) nanoparticles exhibit considerable potential in terms of photothermal properties for bactericidal applications. Nevertheless, the restricted efficacy of their targeted and controlled antibacterial activity has hindered their practical implementation. This study aims to overcome this obstacle by employing chemical modifications to tailor SAs, thereby achieving targeted and light-controlled antimicrobial effects. By conducting atomic-level modifications on palladium SAs using glutathione (GSH) and mercaptophenylboronic acid (MBA), their superior targeted binding capabilities toward Escherichia coli cells are demonstrated, surpassing those of SAs modified with cysteine (Cys). Moreover, these modified SAs effectively inhibit wound bacteria proliferation and promote wound healing in rats, without inducing noticeable toxicity to major organs under 808nm laser irradiation. This study highlights the significance of chemical engineering in tailoring the antibacterial properties of SA nanoparticles, opening avenues for combating bacterial infections and advancing nanoparticle-based therapies.

Ag@AuNP-Functionalized Capillary-Based SERS Sensing Platform for Interference-Free Detection of Glucose in Urine Using SERS Tags with Built-In Nitrile Signal.

A Ag@AuNP-functionalized capillary-based surface-enhanced Raman scattering (SERS) sensing platform for the interference-free detection of glucose using SERS tags with a built-in nitrile signal has been proposed in this work. Capillary-based SERS capture substrates were prepared by connecting 4-mercaptophenylboronic acid (MBA) to the surface of the Ag@AuNP layer anchored on the inner wall of the capillaries. The SERS tags with a built-in interference-free signal could then be fixed onto the Ag@AuNP layer of the capillary-based capture substrate based on the distinguished feature of glucose, which can form a bidentate glucose-boronic complex. Thus, many "hot spots" were formed, which produced an improved SERS signal. The quantitative analysis of glucose levels was realized using the interference-free SERS intensity of nitrile at 2222 cm-1, with a detection limit of about 0.059 mM. Additionally, the capillary-based disposable SERS sensing platform was successfully employed to detect glucose in artificial urine, and the new strategy has great potential to be further applied in the diagnosis and control of diabetes.

Au@Ag@MPBA tags assisted surface-enhanced raman spectroscopy for pathogens detection based on bacteria inhibiting salt-induced aggregation

In this work, a highly structured SERS tags assisted bacteria inhibiting salt-induced aggregation platform was proposed for screening foodborne pathogens. Initially, gold and silver core–shell nanoparticles (Au@Ag NPs) were synthesized by forming an Ag shell on an Au core in situ and employed as SERS substrate. The Au@Ag@MPBA tags were prepared by chemically joining Au@Ag NPs and 4-mercaptophenylboronic acid (4-MPBA) via sulfhydryl groups. 4-MPBA functioned as a bacterial recognition element as well as a Raman reporter molecule. Through the reversible recognition relationship between a boronic acid group of 4-MPBA and bacterial peptidoglycan, multiple types of bacteria were collected by Au@Ag@MPBA tags. Plotting the SERS intensity of the tags against the logarithmic concentration of pathogens (56 ∼ 56 × 105 cfu/mL) revealed an ultra-low detection sensitivity of 16 cfu/mL. Bacteria were determined in real fish samples with satisfactory recoveries (94.26 %∼104.37 %) and validation results (p > 0.05). Thus, the comprehensive bacteria-inhibiting salt-induced aggregation SERS-system offered speedy and accurate pathogenic bacteria screening in actual settings.

Self-Adhesive, Biocompatible, Wearable Microfluidics with Erasable Liquid Metal Plasmonic Hotspots for Glucose Detection in Sweat.

Sweat is a noninvasive metabolite that can provide clinically meaningful information about physical conditions without harming the body. Glucose, a vital component in sweat, is closely related to blood glucose levels, and changes in its concentration can reflect the health status of diabetics. We introduce a self-adhesive, wearable microfluidic chip with erasable liquid metal plasmonic hotspots for the precise detection of glucose concentration in sweat. The self-adhesive, wearable microfluidic chip is made from modified polydimethylsiloxane (PDMS) with enhanced stickiness, enabling conformal contact with the skin, and can collect, deliver, and store sweat. The plasmonic hotspots are located inside the microfluidic channel, are generated by synthesizing silver nanostructures on liquid metal, and can be removed in the alkaline solution. It indicates the erasable and reproducible nature of the plasmonic hotspots. The detection method is based on surface-enhanced Raman spectroscopy (SERS), which allows for accurate detection of the glucose concentration. To enhance the sensitive detection of glucose, the SERS substrate is modified by 4-mercaptophenylboronic acid to achieve the limit of detection of 1 ng/L glucose, which is much lower than the physiological conditions (7.2-25.2 μg/L). The developed microfluidic chip is soft, stretchable, and nontoxic, bringing new possibilities to wearable sweat-sensing devices.

Phenylboronic Acid-Modified Gold Nanoclusters as a Nanoantibiotic to Treat Vancomycin-Resistant Enterococcus faecalis-Caused Infections.

Vancomycin is one of the last lines of defense against certain drug-resistant bacteria-caused infections. However, the high susceptibility to drug resistance and high toxicity seriously limit the application of vancomycin. Nanoantibiotics provide opportunities to solve these problems. Herein, we present mercaptophenylboronic acid (MBA)-modified gold nanoclusters with well-defined molecular formulas and structure (Au44(MBA)18) and excellent antibacterial activities against various drug-resistant bacteria such as vancomycin-resistant Enterococcus faecalis (VRE). Au44(MBA)18 interacts with bacteria by first attaching to teichoic-acid and destroying the cell wall and subsequently binding to the bacterial DNA. Au44(MBA)18 could be administered via multiple routes and has a high biosafety (500 mg/kg, no ototoxicity), overcoming the two major shortcomings of vancomycin (sole administration route and high ototoxicity). Our study is insightful for curing infections caused by multidrug-resistant bacteria using nanoantibiotics with high biosafety.

Smartphone-triggered targeted inactivation of MRSA under SERS monitoring

Silver nanoparticles-based multifunctional agents show tremendous potential for simultaneous imaging and against the methicillin-resistant Staphylococcus aureus (MRSA)-induced superficial infection. However, it is still a challenge to achieve a balance between high precision, high antibacterial efficiency, and biocompatibility. Herein, we present a 4-mercaptophenylboronic acid (4-MPBA)-modified Ag2CO3/Ag2O nano-heterojunctions (AgH@M) that can recognize single MRSA cell by surface-enhanced Raman scattering (SERS) and effectively eradicate MRSA under smartphone irradiation. Moreover, the 4-MPBA molecule acts as triple identities for MRSA targeted binding, SERS tag, and inhibition of excessive release of toxic silver ions for the Raman Imaging guided bacterial treatment. AgH@M simultaneously targeted binding on the surface of bacteria and made full use of the released limited Ag+ into the MRSA, thereby reducing the toxicity to mammalian cells. In addition, the potential antibacterial mechanism involves ROS production from photocatalytic behavior, interference with functional genes of quorum sensing, virulence, biofilm, and ATP-binding cassette transporter. Also, the AgH@M can monitor the residual bacteria in MRSA-infected wounds and keratitis animal models in real-time for at least 7 days by SERS and accomplishes a satisfactory therapeutic effect. This work may provide promising visualized heterojunctions for the targeted eradication of MRSA with a portable light source.

Effect of 4-mercaptophenylboronic acid functionalized MoS2 quantum dots on amyloid aggregation of bovine serum albumin

In recent years, seeking and screening of compounds that can inhibit and/or depolymerize protein aggregation has been a hot issue in the field of pharmaceutical research. As a new material, quantum dots have been widely concerned by medical researchers. In present study, a novel 4-mercaptophenylboronic acid functionalized MoS2 quantum dots (4-MPBA-MoS2 QDs) was successfully synthesized through a one-pot hydrothermal approach by using molybdate dehydrate and 4-mercaptophenylboronic acid as Mo and S source, respectively. Transmission electron microscopy observation showed that the morphology and microstructure of the 4-MPBA-MoS2 QDs displayed uniform spherical shape with a diameter of approximately 1.5 ∼ 3.0 nm. The UV and fluorescence spectra experiments indicated that the prepared QDs had good water solubility and two weak absorption peaks were appeared at 280 nm and 310 nm. When the excitation wavelength was set to 310 nm, the 4-MPBA-MoS2 QDs had the strongest fluorescence intensity, and the maximum emission wavelength appeared at 405 nm. In vitro experiments showed that the 4-MPBA-MoS2 QDs could significantly reduce the aggregation of bovine serum albumin (BSA). Especially when the mass ratio of BSA to 4-MPBA-MoS2 QDs was 1:5, the inhibition rate could reach 76.4%. Cell experiment showed that the presence of 4-MPBA-MoS2 QDs could obviously decrease the cytotoxicity induced by BSA amyloid fibrils. Moreover, the depolymerization of BSA amyloid fibrils by 4-MPBA-MoS2 QDs and its excellent cell permeability were also observed. Molecular docking studies have shown that 4-MPBA-MoS2 QDs may stabilize the BSA structure through van der Waals forces, hydrophobic force, electrostatic interactions and hydrogen bonds formed between the outer layer of 4-MPBA and BSA to prevent fibrosis aggregation. The results of this study suggested that 4-MPBA-MoS2 QDs showed low cytotoxicity, good biocompatibility and solubility, and had a great potential in the design of new drugs for the treatment of amyloid-related diseases.

Synthesis of phenylboronic acid-functionalized covalent organic framework via thiol-ene “click” reaction for highly efficient adsorption of cis-diol containing flavonoids

Owing to tailor-made functionalization, high specific surface areas and tunable pore sizes, covalent organic frameworks (COFs) have been increasingly used in the adsorption area. Herein, a novel COF TzDa-PBA containing phenylboronic acid groups was facilely prepared through a post-modification strategy. The COF TzDa-PBA was synthesized by amine-aldehyde condensation reaction of the 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)trianiline (Tz) and 2,5-diallyloxyterephthalaldehyde (Da-V) through a room-temperature synthetic process to form a vinyl-functionalized COF TzDa-V, followed by covalent linking of 4-mercaptophenylboronic acid (4-MPBA) through the thiol-ene “click” reaction. As a proof-of-concept, the as-obtained TzDa-PBA was used as an adsorbent to adsorb cis-diol containing flavonoids. Representatively, due to its distinctive structure and boronic acid group functional properties, TzDa-PBA showed exceptional adsorption performance for cis-diol containing flavonoids, affording luteolin (LTL) capacity of 219.3 mg g−1, surpassing all those of boronic acid-functionalized materials reported thus far. Furthermore, a commercially available LTL with 85% purity could be easily enriched and further purified by using TzDa-PBA. COF TzDa-PBA with good reusability is promising as adsorbent for selective capture of cis-diol containing flavonoids.

Surface-Enhanced Raman Spectroscopy Combined with External Electric Fields for Non-Invasive Glucose Sensing

Blood glucose detection has been a critical issue in the medical field all over the world for a long time. Especially for diabetic patients, regular monitoring of blood glucose is necessary in their daily life. Nowadays, blood glucose detection mainly relies on fingertip blood glucose meters, which can provide the current blood glucose level in a short period of time. Meanwhile, there are several inconveniences and concerns, including the pain and discomfort of needle-prick blood collection, and the risk of infection at the needle-prick wound. Therefore, many researchers have devoted themselves to the development of non-invasive glucose detection in recent years. Till now, the practical glucose measurement in vivo is still faced with lots of difficulties. To get the signal or response of the molecules in vivo without penetration through the skin layers required two main properties. First of all, the biologic blockage and noise need to be avoided or overcame during the detection. Secondly, it’s necessary to enhance or amplify the signal due to relative low concentration of the target molecule under the skin. Here we introduce a surface-enhanced Raman spectroscopy (SERS) combined with external electric fields to achieve the goal of the detection in vivo without any invasive procedure. In the SERS system, we select 785 nm laser to reach deeper area through the skin layers while preventing the heat effect for tissue damaging. Next, with the signal differences from encountered with various concentration of glucose, 4-mercaptophenylboronic acid (4-MPBA) on silver nanoparticles (AgNPs) is able to quantify the glucose concentrations from the characteristic peak of the Raman shift. Furthermore, the combination with external electric fields induces coagulation of the sensing nanoparticles and provides many hotspots for SERS detection in vivo. We believed that this work is a great stepping stone of real time non-invasive glucose sensing in practical application.

Urchin-Shaped Au-Ag@Pt Sensor Integrated Lateral Flow Immunoassay for Multimodal Detection and Specific Discrimination of Clinical Multiple Bacterial Infections.

A new lateral flow immunoassay strip (LFIA) combining sensitive detection and identification of multiple bacteria remains a huge challenge. In this study, we first developed multifunctional urchin-shaped Au-Ag@Pt nanoparticles (UAA@P NPs) with a unique combination of colorimetric-SERS-photothermal-catalytic (CM/SERS/PT/CL) properties and integrated them with LFIA for multiplexed detection and specific discrimination of pathogenic bacteria in blood samples. Unlike the conventional LFIA that relied on antibody (Ab), this novel LFIA introduced 4-mercaptophenylboronic acid (4-MPBA) as an ideal Ab replacer that was functionalized on UAA@P NPs (UAA@P/M NPs) with outstanding binding and enrichment capacities toward bacteria. Taking Staphylococcus aureus (S. aureus) as model bacteria, the limit of detection (LOD) was 3 CFU/mL for SERS-LFIA, 27 CFU/mL for PT-LFIA, and 18 CFU/mL for CL-LFIA, three of which were over 330-fold, 37-fold, and 55-fold more sensitive than ordinary visual CM-LFIA, respectively. Besides, this SERS-LFIA is capable of identifying three types of bacterial spiked blood samples (E. coli, S. aureus, and P. aeruginosa) effectively according to specific bacterial Raman "fingerprints" by partial least-squares-discriminant analysis (PLS-DA). More importantly, this LFIA was successfully applied to blood samples with satisfactory recoveries from 90.3% to 108.8% and capable of identifying the infected patients (N = 4) from healthy subjects (N = 2) with great accuracy. Overall, the multimodal LFIA incorporates bacteria discrimination and quantitative detection, offering an avenue for early warning and diagnosis of bacterial infection.

Multifunctional AuAg-doping Prussian Blue-based MOF: Enhanced colorimetric catalytic activities and amplified SERS signals for bacteria discrimination and detection

New strategy of a rapid, sensitive bacteria detection is highly desirable. Constructing a dual-mode colorimetric/surface-enhanced Raman scattering (SERS) biosensor is key to obtain highly sensitive discriminating and detecting of different pathogen bacteria with high accuracy. Herein, we developed a multifunctional colorimetric catalytic nanozyme (AuAg@PB MOF) composed of AuAg-doping Prussian Blue analogue-based metal-organic framework (MOF) that fabricated by self-assembled sheet growth of Ag-etched silver-coated gold nanoparticles (Au@Ag NPs) mediated by addition of ferricyanide (K3[Fe(CN)6]). AuAg@PB MOF displays ultrahigh peroxidase-mimicking activity, enhanced colorimetric signal brightness, and notably SERS enhancement. Through optimizing its Fe-doping level, peroxidase-like activity of AuAg@PB MOF is approximately 1900-fold higher than that of horseradish peroxidase (HRP), while its 3-fold enhancement in SERS signal compared with that of gold nanoparticles (Au NPs). Integrated with nanozyme-based sandwich system that made of bacteria/4-MPBA (4-mercaptophenylboronic acid)/AuAg@PB MOF, this dual-modal biosensor achieves a highly sensitive colorimetric assay of bacteria with a lower limit of detection (6 CFU/mL), and simultaneously discriminate E. coli and S. aureus by bacterial “fingerprints” spectra. Furthermore, this proposed colorimetric assay was combined with a smartphone readout-sensing platform for determining bacteria with ultra-sensitivity (2 CFU/mL). This work exhibits a novel colorimetric nanozyme used in dual-mode colorimetric/SERS sensing of bacteria.

Two-dimensional substrate assisted SERS immunosensor for accurate detection of carcinoembryonic antigen

Accurate and sensitive detection of carcinoembryonic antigen (CEA) is essential for the detection of various diseases in healthcare and the medical field. Currently, due to the high false negative rate of CEA assay in clinical setting and its use as a common indicator for early cancer screening, a novel CEA detection method with high sensitivity, increased specificity and the lower cost has become a clinical challenge. Here, a facile sandwich type immunosensor based on surface-enhanced Raman scattering (SERS) was presented including 4-mercaptobenzonitrile (4MBN) labeled gold core-silver shell nanoparticles (Au@4MBN@Ag NPs) as SERS tag and 4-mercaptophenylboronic acid (4-MPBA) functionalized two-dimensional (2D) silver nanoparticle film (Ag FM) as SERS capture substrate for CEA detection. A linearity of 10-9-10-14M was observed with high sensitivity and excellent selectivity for the detection of CEA. Additionally, the spiking experiment yielded 105.33–127.00% recovery with variation coefficients below 10% demonstrating high assay accuracy and precision. The immunosensor we proposed here is a promising approach to quantify CEA in liquid biopsy samples with high sensitivity, which could be further developed for early cancer screening.

A universal boronate affinity capture-antibody-independent lateral flow immunoassay for point-of-care glycoprotein detection

Protein glycosylation and other post-translational modifications are involved in many biological processes including growth, development and immune responses, and glycoproteins are also known as biomarkers for cancer, diabetes and cardiovascular diseases. In traditional lateral flow immunoassay (LFIA) for glycoprotein detection, capture antibody (CA) is often required to label targets. However, the production of CA is complicated and expensive, restricting the wide application of LFIA. In this study, we developed a universal boronate affinity CA-independent LFIA method for glycoprotein detection. 4-Mercaptophenylboronic acid (4-MPBA)-modified Au nanoparticles (namely 4-MPBA-AuNPs) were used as LFIA labels, which could generate colorimetric signal and showed outstanding capability to bind glycoprotein. Compared with CA, 4-MPBA molecular as a glycoprotein recognition element had more prominent advantages, e.g., low cost, easy availability and good quality controllability. Take carcinoembryonic antigen (CEA) as model glycoprotein, the limit of detection of this CA-independent LFIA was 1.25 ng/mL by naked eyes, which was 8-fold lower than conventional CA-dependent sandwich LFIA. Significantly, the developed 4-MPBA-AuNPs-based CA-independent LFIA successfully detected 23 CEA-positive samples from 64 suspected human serum samples within 50 min in a nonlaboratory environment, with a 100% accuracy compared to clinical detection method. Therefore, this diagnostic platform could provide an effective tool for point-of-care glycoprotein detection with excellent reproducibility and high specificity.

Electrochemical sensors based on modified track–etched membrane for non-enzymatic glucose determination

In this research, a non-enzymatic sensor for electrochemical glucose detection based on modified poly(ethyleneterephthalate) track-etched membrane (PET TeMs) was firstly reported in the field of sensing of organic substances. The electrochemical sensors were obtained by photograft polymerization with 2-hydroxyethyl methacrylate (HEMA) and further formation of a polyelectrolyte complex with poly(allylamine) (PAlAm). 4-mercaptophenylboronic acid was functionalized on the surface of PET TeMs via Au-S bond and –OH group of polymerized HEMA to recognize glucose by formation of cyclic boronic ester. The modified PET TeMs were characterized by infrared spectroscopy, gas permeability test, scanning electron microscopy and energy dispersive analysis. Optimal parameters for graft polymerization, such as monomer concentration, polymerization time and distance from the UV-lamp were found. Electrochemical determination of glucose was done by square wave voltammetry. The non-enzymatic sensors for glucose detection showed a good linear relationship between the area under the oxidation peak and glucose concentration in the range from 0.1 mM to 8 mM with a low detection limit of 0.1 mM (R2 = 0.999). In addition, the sensors showed excellent reproducibility, repeatability and good selectivity for metal ions and ascorbic acid. The determination of glucose in apple juice and human blood serum demonstrated that the obtained sensors can be used in real samples with sufficient reproducibility of results.

Ti3C2Tx MXene -facilitated non-selective trapping effect: Efficient SERS detection of exosomal PD-L1

Biosensors developed through a sandwich approach have demonstrated favorable detection performance for exosomal programmed cell death 1 ligand 1 (ExoPD-L1) detection. However, the reported PD-L1 antibodies, peptides, and aptamers utilized in these biosensors typically bind to the extracellular region, with overlapping binding sites that severely constrain the fabrication of biosensors. In this study, we present a simple approach to specifically identify and analyze ExoPD-L1 through the non-selective trapping effect of Ti3C2TX (X=-O, -F, -OH) MXene on exosomes via the formation of Ti–O–P complexation, and the selective capture of peptide-functionalized Au@MPBA (4-Mercaptophenylboronic acid) @SiO2 surface enhanced Raman scattering (SERS) tags on ExoPD-L1. The biosensor delivered a both hypersensitive and reliable performance in exosome detection with a low limit of detection (20.74 particles/mL) in the linear range of 102 to 5×106 particles/mL. Furthermore, the biosensor demonstrated excellent stability and interference resistance in detecting ExoPD-L1 in clinical serum samples, enabling the easy differentiation of breast cancer patients from healthy controls. This work provides new insights into the design of biosensors for exosome detection and can serve as a replicable template for sandwich immunoassay detection for other types of sensors, including but not limited to SERS.

Sensitive Determination of Stevioside by Surface-Enhanced Raman Spectroscopy (SERS) Using 4-Mercaptophenylboric Acid Functionalized Silver Nanoparticles (Ag NPs)

Stevioside is an important natural sweetener in food and beverages. There are concerns about its safety, but few methods for its determination. Silver nanoparticles (Ag NPs) functionalized with 4-mercaptophenylboronic acid (4-MPBA) were successfully used to determine stevioside in beverages based upon surface-enhanced Raman spectroscopy (SERS). The Ag NPs self-assemble with 4-MPBA through the covalent interaction of their sulfhydryl groups with the metal particles. Boronic acid groups bonded to 1,2-/1,3-diol groups form cyclic boronic esters with strong affinity and significant specificity for stevioside. The combination of the two leads to an alteration of the 4-MPBA vibrational mode. The change in the orientation of the moiety and the charge transfer resulted in a significant increase of the SERS signal. The substrates showed strong specificity and sensitivity to stevioside in the presence of other sweeteners. Also, the substrate modification conditions were optimized, including the time, ratio, and concentration. The limit of detection (LOD) for stevioside in beverages was 0.210 μmol/L, and the recovery was from 98.4% to 109.4%. In summary, the presented SERS method provides high sensitivity for stevioside.

Electrochemical detection of lead and cadmium ions in water by sensors based on modified track-etched membranes

Electrochemical sensors based on PET track-etched membranes (TeMs) were prepared by photograft polymerization of 2-hydroxyethylmethacrylate (HEMA) and subsequent formation of interpolyelectrolyte complexes with poly(allylamine) (PAlAm). The functionalized TeMs were characterized by scanning electron microscopy (SEM), FTIR spectroscopy, gas permeability and colorimetric assay. Parameters of graft polymerization such as monomer concentration, time of irradiation, solvent and others were estimated and optimized. Cd(II) and Pb(II) ions were detected by using square wave anodic stripping voltammetry (SW-ASV). Additional modification of the modified membranes with 4-mercaptophenylboronic acid (MPBA) led to increasing of stability of the sensors. The linear range for the detection of Cd(II) and Pb(II) ions using the modified electrode was 50 µg - 4.25 mg/L and 10 µg – 4.25 mg/L. Moreover, the obtained results of SW-ASV demonstrated that the enhancement in the electrochemical signals was achieved with PET TeMs-g-PHEMA-PAlAm\MPBA compared to that of a bare PET TeMs-g-PHEMA. Selectivity test showed that alkali and alkaline earth metal ions, except for magnesium (up to 1 mg/l), do not particularly interfere with the determination of lead and cadmium in the analyte. Sensing of Pb and Cd ions in river water demonstrate us that prepared sensors can be used in real conditions with sufficient accuracy and reproducibility of the results.

Quantitative detection of dopamine in human serum with surface-enhanced Raman scattering (SERS) of constrained vibrational mode

Dopamine (DA) is a crucial neurotransmitter involved in the hormonal, nervous, and vascular systems being considered as an index to diagnose neurodegenerative diseases, including Parkinson's and Alzheimer's disease. Herein, we demonstrate the quantitative sensing of DA using the peak shift in surface-enhanced Raman scattering (SERS) of 4-mercaptophenylboronic acid (4-MPBA), resulting from the concentration of DA. To enable the signal enhancement of Raman scattering, Ag nanostructure was built with one-step gas-flow sputtering. 4-MPBA was then introduced using vapor-based deposition, acting as a reporter molecule for bonding with DA. The gradual peak-shift from 1075.6 cm−1 to 1084.7 cm−1 was observed with the increasing concentration of DA from 1 pM to 100nM. The numerical simulation revealed that DA bonding induced a constrained vibrational mode corresponding to 1084.7 cm−1 instead of a C–S-coupled C-ring in-plane bending mode of 4-MPBA corresponding to 1075.6 cm−1. Proposed SERS sensors depicted reliable DA detection in human serum and good selectivity against other analytes, including glucose, creatinine, and uric acid.