4-mercaptophenylboronic Acid Research Articles

An electrochemiluminescence sensor of magnetic glycosyl-imprinted microspheres based on multi-probe signal amplification for CD44v6 determination

A CD44v6 detection method was developed by using glycosyl-imprinted technique and enhanced with multi-probe signal amplification. Oligomeric hyaluronic acid was used as the template molecule, which was prepared by the cleavage of polyhyaluronic acid using hyaluronidase. Mercaptophenylboronic acid was self-assembled on the surface of core-shell [email protected]3O4 magnetic microspheres through the covalent interaction between its thio group and Au. Then oligomeric hyaluronic acid (<10 kDa) was linked on [email protected]3O4 via the formation of a cyclic ester between boronic acid and the ortho-dihydroxy group of oligomeric hyaluronic acid. By using oligomeric hyaluronic acid as a template and p-aminophenylboronic acid (p-APBA) as the functional monomer, boronate affinity glycosyl-imprinted polymer films were prepared on [email protected]3O4 by chemical polymerization. The magnetic glycosyl-imprinted polymer microspheres (MGIP) were attached on the surface of the magnetron-controlled glassy carbon electrode (MGCE) as the recognition component rebinding for the template, and CD44v6 was specifically recognized by the binding of the imprinted cavities to the oligomeric hyaluronic acid. The boronic acid functionalized tris-(2,2’-bipyridyl) ruthenium (II) (Ru(bpy)3-BO3) was used as a molecular probe to label the adsorbed oligomeric hyaluronic acid of CD44v6. With the aid of the multiply captured Ru(bpy)32+ probes on CD44v6 and the high luminescence efficiency of Ru(bpy)32+, the electrochemiluminescence response of the sensor exhibits a high sensitivity for CD44v6 determination with a detection limit of 0.08 ng/L. The method was applied in the assay of CD44v6 in serum samples.

Construction of Boronate-Affinity Magnetic Immunity SERS Sensor and Detection of Alpha-Fetoprotein (AFP) in Human Serum

Abstract According to its characteristics, borate can recognize and adsorb target glycoproteins and specific binding properties of antigens and antibodies. This article introduces a preparation method for a magnetic immune SERS sensor, and it is used for the specific identification and detection of trace AFP in human serum. The test used AFP as the target protein and 4-mercaptophenylboronic acid (4-MPBA) modified gold-coated silver nanoparticles (Ag@AuNPs) as the signal factor. After the AFP antibody was grafted on the boric acid group, the SERS detection probe (Ag@Au@4-MPBA@Anti-AFP) was obtained. On the surface of boric acid-functionalized (-P) magnetic silica particles, AFP antibody was modified, and the particles were used as magnetic immunocapture probes (Fe3O4@SiO2-P@Anti-AFP). Finally, the sandwich structure complex of “detection probe-target protein-capture probe” was successfully constructed. The prepared magnetic immune SERS sensor exhibits excellent selectivity and high sensitivity for AFP detection; based on the signal-to-noise ratio S/N = 3, the detection limit can reach 1.0 ng/mL; by performing a spike test on AFP in human serum, the sensor can be used to detect AFP in actual samples. The recovery rate was between 85.8% and 105.7%, and the RSD distribution was ≤3.52%. The sensor was easy to prepare, required no complex processing of samples and can achieve rapid detection, so that it is expected to become a new strategy for clinical detection of AFP.

Ag-Nanowire Bundles with Gap Hot Spots Synthesized in Track-Etched Membranes as Effective SERS-Substrates

This paper presents a cost-effective approach for the template-assisted electrodeposition fabrication of substrates for surface-enhanced Raman scattering (SERS) with metal nanowires (NWs) grown in pores of polymer track-etched membranes (TM). This technique allows the synthesis of NWs array with its certain surface density and diameter (from dozen to hundreds of nm). NWs length also may be varied (order of μm) by controlling deposition time. Here we grow vertical Ag-NWs which are leaning towards their nearest neighbors, forming self-assembled bundles whose parameters depend on the NW aspect ratio (length to diameter). We show that in such bundles there are “hot spots” in the nm-gaps between NWs tips. Computer simulations have demonstrated a strong enhancement of the electric field within these hot spots; thus, the Raman signal is markedly amplified for analyte molecules placed directly inside the gaps. We have experimentally proved the potential of this SERS-technique on the example of 4-Mercaptophenylboronic acid (4-MPBA). For 4-MPBA the maximal enhancement of Raman signal was found at NWs length of ~1.6 μm and diameter of ~100 nm. The effect is higher (up to twice) if “wet” substrate is used just immediately after the TM polymer removal so that the tips are brought to lean after analyte exposure. We suggest this new type of nanostructured SERS-substrates as a base of effective sensing of extremely low concentration of analytes.

Integrated SERS Platform for Reliable Detection and Photothermal Elimination of Bacteria in Whole Blood Samples.

Herein, an interference-free surface-enhanced Raman scattering (SERS) platform with a "sandwich" structure has been developed for reliable detection and photothermal killing of bacteria with whole blood as the real sample. The multifunctional platform comprised a plasmonic gold film (pAu) functionalized with bacteria-capturing units of 4-mercaptophenylboronic acid and internal reference of 4-mercaptobenzonitrile as the SERS substrate and vancomycin-modified core (gold)-shell (Prussian blue) nanoparticles (Au@PB@Van NPs) as the SERS tag. The detected SERS signals were from the Raman-silent region where no background signals occurred from biological sources, eliminating the interference and improving the detection sensitivity and accuracy. As a proof-of-concept, model bacterial strain, Staphylococcus aureus, was captured and detected in the whole blood samples. Furthermore, high antibacterial efficiency of approximately 100% was reached under the synergistic photothermal effect from pAu and Au@PB@Van NPs. This study provides a new avenue for bacteria detection in real samples and their subsequent in situ elimination.

Preparation of 4-mercaptophenylboronic acid functionalized two-dimensional molybdenum disulfide nanocomposite and its specific enrichment for N-glycopeptide

Protein N-glycosylation plays a crucial role in the folding, transportation, and localization of proteins, and participates in many important biological processes such as receptor activation and signal transduction. An increasing number of studies have shown that abnormal protein glycosylation is closely related to various diseases. Therefore, N-glycosylated proteins are potential candidates for become new biomarkers or drug targets. The current research strategy for N-glycosylated proteins is to first digest the protease into peptides and then identify them by mass spectrometry. In sample preparation processing, enrichment and separation of N-glycopeptides have become the vital step for glycoproteomic analysis. However, because of their low abundance and poor ionization, mass spectrometric identification of N-glycopeptides in complex samples remains a challenging task. Therefore, the development of a selective enrichment strategy for N-glycopeptides from complex biological samples is necessary. In this work, new functional nanomaterials were prepared through a simple, convenient, and efficient two-step "Au-S" reaction. In short, the "Au-S" bond was first used to load nano-gold wires on the surface of molybdenum disulfide (MoS2), and then to connect these wires to 4-mercaptophenylboronic acid (4-MPB). The resulting nanomaterial named MoS2/Au/4-MPB was successfully prepared by serial functionalization of ultra-thin two-dimensional MoS2, nano-gold wires and 4-MPB for the efficient enrichment of N-glycopeptides. The layered structure of molybdenum disulfide nanomaterials can provide numerous modifiable sites for the reaction, allowing for convenient modification of the nano-gold wires. The functional group 4-MPB has high affinity for N-glycopeptides, and it can selectively enrich them in biological samples. In order to evaluate the N-glycopeptide enrichment performance of MoS2/Au/4-MPB, standard proteins human immunoglobulin G (IgG) and bovine serum albumin (BSA) trypsin digests were used. Thus, facilitated interactions with N-glycopeptides for boric acid-based retention could be expected. Low femtomolar detection sensitivity, 1:1000 enrichment selectivity, and 100 μg/mg loading capacity were achieved for N-glycopeptide enrichment. In the application of this material to biological samples, exosomes were chosen as the research objects. On the one hand, exosomes serve as a new class of carriers for intercellular communication and drug delivery. Almost all types of cells can secrete exosomes. On the other hand, urine is another potential source for liquid biopsy samples in addition to blood. Obtaining urine samples is a less invasive process, and urine samples are easier to handle and save as compared to blood samples. Exosomes can also be detected in urine. Cell-specific components such as proteins, lipids, and nucleic acids can provide diverse information, which is of great significance in disease diagnosis and treatment. However, there are only a few studies on urinary exosomes N-glycoprotein group. In this research, N-glycoproteins were successfully identified in urine exosomes. In three replicate experiments, 536, 515 and 487 N-glycosylated peptides were identified from 279, 270 and 279 N-glycoproteins, respectively. After de-duplication of the three sets of data, a total of 768 N-glycopeptides corresponding to 377 N-glycoproteins were identified. This result indicates that the novel nanocomposite has good enrichment selectivity and sensitivity for N-glycopeptides enrichment in complex biological samples, and this method provides a new method for glycoproteomics research.

Electrochemical non-enzymatic sensing of glycoside toxins by boronic acid functionalized nano-composites on screen-printed electrode

Natural glycoside toxins, one of the most ubiquitous toxins in food of plant origin, cause serious health threat on humans and livestock. Evaluation of their health risk is of great significance. We proposed a non-enzymatic sensor based on reduced graphene oxide/gold nanoparticles/boronic acid nano-composites for their rapid and simple detection. The nano-composites were integrally synthesized in liquid dispersion. Gold nanoparticles, which were reduced from chloroauric acid, nucleated and grew on graphene oxide films directly. 4-mercaptophenylboronic acid self-assembled with gold nanoparticles through gold-sulfur bond. With reduction of graphene oxide through cyclic voltammetry, the nano-composites were then one step modified onto the working electrodes as sensing layer. Glycoalkaloids, common glycoside toxins in potatoes, were detected with the functionalized screen-printed electrodes. Electrochemical differential pulse voltammetry was applied for the detection. The sensor exhibited good stability in at least four weeks with a wide detection range from 10 μM to 1000 μM. The limit of detection was as low as 3.4 μM. The developed sensor was successfully applied to the detection of glycoalkaloids in real potato samples. As a proof of concept, the disposable sensor with high sensitivity and selectivity exhibited great application potential for the risk control of natural glycoside toxins in food.

Mercaptophenylboronic Acid-Activated Gold Nanoparticles as Nanoantibiotics against Multidrug-Resistant Bacteria.

Multidrug-resistant (MDR) bacteria-induced infections are becoming challenging issues threatening human health and life. Current antibiotics can hardly tackle this problem. Herein, we present a strategy to prepare mercaptophenylboronic acid (MBA)-activated gold nanoparticles (Au NPs) as an antibacterial agent against MDR bacteria. Both Au NPs and MBA cannot serve as antibiotics. However, when MBA attaches on Au NPs, the Au_MBA NPs show potent antibacterial activities against Gram-positive MDR clinical isolates (e.g., MDR Staphyloccocus aureus, MDR S. aureus; MDR Staphyloccocus epidermidis, MDR S. epidermidis). Furthermore, Au_MBA NPs show an extremely high median lethal dose (LD50,i.v., 960 mg/kg), which is much higher than those of most of the clinically used antibiotics. As an application example, we dope Au_MBA NPs with electrospun poly(ε-caprolactone) (PCL)/gelatin nanofibrous membranes as wound dressings, which show striking ability to remedy S. aureus- or MDR S. aureus-infected full-thickness skin wounds on rats. Our study provides a novel strategy for treating MDR bacteria-infected wounds in a simple, low-cost, and efficient way, which holds promise for broad clinical applications.

Combination of bacitracin-based flocculant and surface enhanced Raman scattering labels for flocculation, identification and sterilization of multiple bacteria in water treatment

Bacteria, especially antibiotic-resistant bacteria, in water threaten public health in countries. Simultaneous flocculation, sterilization and identification of bacteria are great challenge in water treatment. Herein we presented a three-in-one compound through combining a novel Bacitracin-based flocculant (B-g-PAMDAC) and surface enhanced Raman scattering (SERS) labels, the modified Au@AgNPs using graphene oxide (GO) and 4-mercaptophenylboronic acid (4-MPBA). B-g-PAMDAC with bactericidal groups and microblock structure was synthesized via copolymerization and self-assembly. Its functional groups and microblock structure contributed to the excellent performance in flocculation of bacteria. 4-MPBA as bacterial capture bound to the bacterial cell membrane and contributed to recognition of bacteria in flocculation. Bacteria aggregating around Au@AgNPs resulted in abundant “hot spots” and strong Raman signals. SERS labels obviously improved the sensitivity, accuracy and stability of bacteria identification even at low bacterial concentration of 1 × 103 CFU mL−1. They presented distinct fingerprints of bacteria, Escherichia coli, Pseudomonas aeruginosa, Bacillus cereus and Enterococcus faecalis, in Raman mappings. Bacitracin improved sterilization efficiency of B-g-PAMDAC in four bacteria treatment in terms of sterilization rate and time. β-galactosidase and respiratory activity of bacteria revealed sterilization mechanism of B-g-PAMDAC that changed permeability of cell membrane before it reduced the respiration activity of bacteria and ruptured cell wall.

Photoelectrochemical immunosensor for methylated RNA detection based on WS2 and poly(U) polymerase–triggered signal amplification

A novel photoelectrochemical immunosensor has beenconstructed for the determination of methylated RNA. MoS2 nanosheets with large specific area were employed as photoactive material, gold nanoparticles were used as signal amplification unit and immobilization matrix of 4-mercaptophenylboronic acid, anti-m6A antibody was adopted as methylated RNA recognition reagent, and poly(U) polymerase-mediated RNA chain extension and Ru(NH3)63+ were used as assisted signal amplification unit. With the sensitization effect of Ru(NH3)63+, the photoactivity of WS2 nanosheets was improved greatly, which also improved the sensitivity. Using visible-light excitation and ascorbic acid as electron donor, the sensitive determination of methylated RNA was achieved by monitoring the photocurrent change with different concentrations of methylated RNA. This photoelectrochemical immunosensor hasa wide linear relationship with methylated RNA concentration from 0.05 to 35nM under optimal experimental conditions. The low detection limit of 14.5pM was realized based on 3σcriterion. In addition tothe good selectivity, this sensor also presents highreproducibility with arelative standard deviation of 1.4% for the photocurrent of seven electrodes. The applicability of the developed method was also investigated by detecting the level of methylated RNA in corn seedling leaves with and without sulfadiazine treatment. Graphical abstract A novel photoelectrochemical immunosensor was developed for methylated RNA detection using the photoactive material of MoS2 and poly(U) polymerase-mediated RNA chain extension.

Ultrasensitive sandwich-like electrochemical biosensor based on core-shell Pt@CeO2 as signal tags and double molecular recognition for cerebral dopamine detection

In this report, 4-mercaptophenylboronic acid (MBA) and dithiobis (succinimidyl propionate) (DSP) were used as DA molecular recognizer, which bounded onto the prepared Pt@CeO2 nanomaterial and the electrode surface. A sandwich-like electrochemical biosensor was constructed for sensitive detection of dopamine (DA) based on double molecular recognition and Pt@CeO2 (MBA-DSP- Pt@CeO2) as an electrochemical probe for signal amplification. It is worth noting that the diol and amine groups of DA were reacted by the boronic acid of MBA and the succinimide residue of DSP, respectively. This sandwich-like double molecular interaction can efficiently and accurately identify DA. The uniform Pt@CeO2 multicore@shell nanospheres as signal tags and signal amplifiers in electrochemical biosensor were synthesized by hydrothermal, which has excellent catalytic activity for H2O2. Interestingly, more oxygen vacancies were produced in the lattice structure of CeO2 doped with Pt, so that the catalytic and redox performance of the obtained Pt@CeO2 was much better than that of pure CeO2, thus greatly improving the performance of the proposed sensor. The proposed electrochemical biosensor provided a wide detection range of 2–180 nM and a low detection limit (0.71 nM) by the electrochemical measurement. And it also showed ultra-high sensitivity, accuracy and broad application prospect, which developed a new research method for early clinical diagnosis.

Magnetic bead-based electrochemical and colorimetric methods for the detection of poly(ADP-ribose) polymerase-1 with boronic acid derivatives as the signal probes

Poly(ADP-ribose) polymerase-1 (PARP-1), as a highly conserved nuclear enzyme, can catalyze the transfer of multiple ADP-ribose units from β-nicotinamide adenine dinucleotide (NAD+) to substrate proteins, including PARP-1 itself. In this work, two boronic acid derivatives, ferroceneboronic acid (FcBA) and 4-mercaptophenylboronic acid (MPBA) were used as the signal probes for electrochemical and colorimetric detection of PARP-1, respectively. The detection platform was constructed by modification of double-stranded DNA (dsDNA) on the surface of magnetic beads (MBs). Once PARP-1 was captured by the MB-dsDNA, auto-PARylation was initiated and the PAR products consisting of abundant ribose units were covalently bound to FcBA or MPBA through the formation of boronate ester covalent bonds. Sequestration of FcBA or MPBA by the PAR-covered MBs led to the decrease in the electrochemical signal of FcBA or preventing the MPBA-triggered aggregation of gold nanoparticle indicators. The change of oxidation current or adsorption intensity (color) was dependent upon the concentration and activity of PARP-1. A wide linear range of 0.1 ∼ 50 U was obtained for the electrochemical or colorimetric assays. The methods have been used to evaluate the inhibition efficiency and monitor the PARP-1 activity in living and apoptotic cancer cells.

Surface-enhanced Raman spectroscopy in tandem with a gradient electric field from 4-mercaptophenylboronic acid on silver nanoparticles.

The surface-enhanced Raman spectroscopy (SERS) signal of a reporter on silver nanoparticles can be effectively gained by gradient electric field application. The external electric field initiates the dielectrophoresis of nanoparticles and their electrically induced dipole-dipole interaction. Owing to dielectrophoresis, the nanoparticles are concentrated in the area of high electrical field strength. The induced dipole-dipole interaction leads to additional coagulation of nanoparticles and formation of hotspots. Both dielectrophoresis and induced dipole-dipole interaction increase the number of hotspots, which leads to a SERS signal growth. These two mechanisms of SERS signal amplification are explained by the dielectrophoresis and Derjaguin-Landau-Verwey-Overbeek theories. The benefits of the surface-enhanced Raman spectroscopy in tandem with the gradient electric field are experimentally confirmed using a SERS-active reporter, 4-mercaptophenylboronic acid which has a characteristic peak at Raman shift of 1586cm-1, conjugated to silver nanoparticles of 32, 52, 58, and 74nm in diameter. The SERS signal gain depends on the silver nanoparticle stability, size, and electric field strength. The limit of detection for 4-mPBA in the system under study can be calculated from the concentration plot and equals to 63nM. The enhancement factor calculated for SERS in tandem with the gradient electric field can reach 106.Graphical abstract.

Magnetic bead-based electrochemical and colorimetric assays of circulating tumor cells with boronic acid derivatives as the recognition elements and signal probes

Simple, sensitive and rapid detection of circulating tumor cells (CTCs) is of great importance for early diagnosis and therapy of cancers. Overexpression of sugar units on cell surface is related to the phenotypes of many cancers. Based on the boronate ester interaction, we reported the electrochemical and colorimetric detection of CTCs with high simplicity and sensitivity. Specifically, ferroceneboronic acid (FcBA) can be measured by differential pulse voltammetry and 4-mercaptophenylboronic acid (MPBA) can induce the aggregation and color change of gold nanoparticles (AuNPs). CTCs captured by the aptamer-modified magnetic beads (Apt-MBs) can sequestrate FcBA or MPBA molecules by the formation of boronate ester bonds, thus leading to the decrease in the electrochemical signal of FcBA or preventing the MPBA-triggered aggregation of AuNPs. Due to the overexpression of sugar groups on the surface of CTCs, the amplification-free methods exhibited high sensitivity and obviated the use of additional antibody or aptamer for the recognition of captured cells. With MCF-7 cancer cell as the model, 50 cells can be readily determined by the electrochemical and colorimetric methods. The proposed strategy is valuable for probing of cell glycosylation and designing of novel sensing devices for detection of sugar-containing biological macromolecules and cells.

Simultaneous use of phenylboronic acid as a phase transfer agent and targeting ligand for gold nanoparticles

Herein, we have rationally utilized 4-mercaptophenylboronic acid (4-MPBA) as a hydrophilic ligand for phase transfer of gold (Au) NPs from non-hydrolytic system into aqueous solutions and as a targeting ligand for recognition of model pathogen. In principle, while free thiol end of 4-MPBA conjugates to surface of hydrophobic Au NPs to form stable Au NP in aqueous solutions, diol groups can bind to glycan on the membrane of pathogens through cis-diol configuration. Finally, this ligand can be applied to other hydrophobic metallic and metel oxide NPs for phase transfer and molecular recognition.

A novel Wulff‐type boronate acid‐functionalized magnetic metal‐organic framework imprinted polymer for specific recognition of glycoproteins under physiological pH

Boronate affinity molecularly imprinted materials have been widely used for the separation of glycoproteins under alkaline conditions that is not conducive to the structural stability of the protein. In this work, a kind of novel molecularly imprinted polymer (MIP/TBA/MOF@Fe3 O4 ) was prepared via grafting self-assembled molecular team of boronic acids on the surface of the magnetic metal-organic framework core. The teamed boronate affinity was formed by 2-mercaptoethylamine and 4-mercaptophenylboronic acid for specific separation of glycoproteins under physiological pH (pH7.4). The obtained nanoparticles show high binding capacities (337.8mg/g), fast adsorption equilibrium time (20min), and good specificity (imprinting factor, 4.52) for glycoproteins under physiological pH. Furthermore, the prepared imprinted polymer still shows good adsorption capacity for glycoprotein after five times of repeated use, and its adsorption capacity only dropped by 4.7%. More importantly, the prepared nanoparticles have good potential to adsorb glycoproteins from real biological samples.

Analyte-triggered autoacceleration of 4-mercaptophenylboronic acid-mediated aggregation of silver nanoparticles for facile and one-step ratiometric colorimetric method for detection of ascorbic acid

A simple, fast, one-step method is described for ratiometric colorimetric detection of ascorbic acid (AA) based on 4-mercaptophenylboronic acid (4-MPBA) and silver nanoparticles (AgNPs). In the presence of AA, the aggregation process of AgNPs can be triggered and accelerated, due to the interaction between 4-MPBA and the cis 1,2-diol moieties of AA through a reversible esterification, resulting in a distinguish color change from yellow to brownish red. The AA concentration-dependent color change can be quantified by the bare eyes or a UV–Vis spectrometer. The whole AA detection procedure was able to complete in 10 min with an excellent linear relationship (1–500 μM) and a low limit of detection (0.70 μM). The proposed approach was also used to accurately evaluate AA levels in orange juice. In our perception, this assay is rapid, sensitive, and specific, which demonstrates its potential on constructing biochemical and clinical sensors.

Localized surface plasmon resonance coupled single-particle galactose assay with dark-field optical microscopy

Galactosemia as a metabolic disease is associated with the increase of galactose concentration in blood. Hence, it is important to detect the amount of galactose for the early discovery of diseases. In this study, we demonstrate a convenient and sensitive localized surface plasmon resonance (LSPR) coupled method for the quantification of galactose by single- particle detection (SPD) with dark-field optical microscopy (DFM). The design is based on the specific boronate affinity interaction between the boronic acid ligands and cis-diol groups. The mercaptophenylboronic acid (MPBA) functionalized gold nanoparticles (MPBA-GNPs) served as the signal probe were prepared. In the presence of galactose, MPBA can react with the cis-diol groups of the galactose, resulting in the occurrence of MPBA-GNPs plasmon oscillations coupling and the apparent change of particle scattering color from green to yellow. By quantifying the ratio of yellow particles by SPD with DFM, the trace amount of galactose in solution can be accurately detected. Limit-of-detection (LOD) as low as 0.83 nM is achieved in the linear range of 1–75 nM, which is more sensitive than that of the previous reported ensemble measurement methods. The satisfactory spike recoveries in human urine sample are successfully obtained, which indicates the potential applications of this proposed method in practical sample. As a consequence, this study provides a prospect platform for the ultra-sensitive biomolecules detection in the future.

Raman reporter-assisted Au nanorod arrays SERS nanoprobe for ultrasensitive detection of mercuric ion (Hg2+) with superior anti-interference performances

Ultra sensitive detection of mercuric ion (Hg2+) with superior anti-interference capability from natural water is of great significance for food safety, environmental protection, and human health. We herein develop Au ordered nanorod arrays (Au NRAs) as surface-enhanced Raman scattering (SERS) substrates to construct SERS-active and signal-reproducible sensing platforms modified with 4-mercaptophenylboronic acid (4-MBA) as multifunctional SERS reporters. The aqueous Hg2+ can be efficiently trapped by 4-MBA through electrophilic substitution reactions and precisely appraise its concentration based on the collective spectral changes of reporters including peak disappearance, emergence, and Raman shift. Based on this, the optical nanoprobe shows an ultrahigh detection sensitivity of 0.1 nM for Hg2+, which is two orders of magnitude lower than the U.S.A. environmental protection agency (EPA)-required maximum level of drinkable water. It also offers both an exceptional Hg2+ discrimination against other metal ions as well as organic ligands and perfect feasibilities of detecting solutions with ultra-wide pH ranges from 1.0–14.0 at varying temperatures. Moreover, the nanoprobe demonstrates an ability to identify different chemical forms of mercury and has a high repeatability, accuracy and reliability to meet the practical detection requirements in natural environments.

Synthesis of Cu–Ag core–shell nanoparticles as highly active surface-enhanced Raman scattering substrates for sensitive detection of caffeic acid

Core–shell nano-metal structures as SERS probes have drawn attention and have been applied to detecting analytes at low concentrations. Here, we have developed a novel SERS probe composed of Cu–Ag for the quantitative, rapid and ultrasensitive detection of caffeic acid. The surface of Cu–Ag was modified with 4-mercaptophenylboronic acid (4-MPBA) to allow the probe to detect caffeic acid, wherein 4-MPBA specifically binds to caffeic acid by an esterification reaction. The results obtained in this work show that the SERS performance of the 4-MPBA substrate is better than that of the Cu–Ag substrate. To determine the binding of caffeic acid to 4-MPBA, the B-OH stretching vibration at 1170 cm–1 was selected as the representative signal. It was found that there is a linear relationship between the intensity of the peak at 1170 cm–1 and the concentration of caffeic acid.

Double molecular recognition strategy based on boronic acid-diol and NHS ester-amine for selective electrochemical detection of cerebral dopamine.

Electrochemical detection of dopamine (DA) usually depends on electrochemical oxidation of DA. This conventional method can hardly provide sufficient sensitivity and selectivity in the determination of the cerebral DA down to nanomolar level, because the ability of DA to be electrochemically oxidized is limited and many electroactive interferents are also oxidized at a similar potential with DA. Here, an electrochemical assay based on a double molecular recognition strategy has been proposed and proved to be of high sensitivity and selectivity for DA measurement in the cerebral system. 3,3'-Dithiodipropionic acid di(N-hydroxysuccinimide ester) (DSP) was anchored on the electrode surface to capture DA target through the specific reaction between N-hydroxysuccinimide (NHS) ester and amine. The captured DA endowed the electrode with a layer of diol groups, which further reacted with the boronic acid to trap of 4-mercaptophenylboronic acid (MBA) molecules, thus leading to the conjunction of electroactive thionine (Th) molecules on the electrode for signal readout. In addition, an Au nanostructure was employed to enhance signal amplification and facilitate the double molecular recognition process. As a consequence, this method was able to quantify DA from 1 to 300nM with a detection limit of 0.74nM, which exhibited a high specificity against cerebral interferents. Furthermore, the practicability of this platform was successfully demonstrated through determination of the dynamics of cerebral DA in the events of high K+ and nomifensine retromicrodialysis. Graphical abstract.