The authors describe an aptamer-based fluorometric assay for the insecticide acetamiprid. It is based on target-induced release of the fluorescein-labeled complementary strand of the aptamer (CS) from the aptamer/CS conjugate (dsDNA). Three kinds of nanoparticles with opposite effects on the fluorophore (FAM) were used. These include gold nanoparticles (AuNPs), single-walled carbon nanotubes (SWNTs) and silica nanoparticles (SiNPs) coated with streptavidin. In the presence of acetamiprid, FAM-labeled CS is released from the dsDNA-modified SNP-streptavidin complex and accumulates in the supernatant (phase I) after centrifugation. Fluorescence intensity decreases on addition of the supernatant to the SWNTs and AuNPs because they act as quenchers (phase II). In the absence of acetamiprid, the dsDNA-modified SiNP-streptavidin complex remains intact and no labeled CS is present in the supernatant containing the AuNPs and SWNTs. So, the relative fluorescence intensity is quite low. The assay is highly selective for acetamiprid and has a limit of detection (LOD) as low as 127 pM. The method was successfully applied to the determination of acetamiprid in spiked serum and water where it gave LODs of 198 and 130 pM, respectively.
Graphical abstract In the absence of acetamiprid, the dsDNA-modified silica nanoparticle (SiNP)-streptavidin conjugate remains intact, leading to a very weak relative fluorescence intensity. In the presence of target, the dsDNA-modified SiNP-streptavidin complex is disassembled and FAM-labeled CS is released from the aptamer (Apt), resulting in a very strong relative fluorescence intensity.
The authors describe a method for the fabrication of a nanohybrid composed of carbon dots (C-dots) and gold nanoparticles (AuNPs) by in-situ reduction of C-dots and hydroauric acid under alkaline conditions. The process does not require the presence of surfactant, stabilizing agent, or reducing agent. The hybrid material was deposited in a glassy carbon electrode (GCE), and the modified GCE exhibited good electrocatalytic activity toward the oxidation of nitrite due to the synergistic effects between carbon dots and AuNPs. The findings were used to develop an amperometric sensor for nitrite. The sensor shows a linear response in the concentration range from 0.1 μmol?L-1 to 2 mmol?L-1 and a low detection limit of 0.06 μmol?L-1 at the signal-to-noise ratio of 3.
Graphical abstract Fabrication, characterization and electrochemical behavior of a glassy carbon electrode modifid with carbon dots and gold nanoparticles for sensing nitrite in lake water.
The authors describe a method for signal amplification in electrochemical aptasensors. It is based on the induction of an increased electrochemical current by the aptamer captured on a glassy carbon electrode (GCE). The phosphate groups on the aptamer backbone are brought to reaction with added molybdate to form a redox-active molybdophosphate precipitate on the surface of the GCE that generates a strong electrochemical current. To further enhance sensitivity, gold nanorods (GNRs) were selected as a support for the immobilization of aptamers. The aptasensor was applied to the determination of the cancer biomarker carcinoembryonic antigen (CEA) in a sandwich format. Antibody against CEA, CEA (antigen) and GNRs modified with CEA aptamer were sequentially captured on the GCE. The resulting aptasensor, best operated at a voltage as low as 0.18 V vs. Ag/AgCl, is highly sensitive and has a wide linear range that extends from 0.1 pg·mL?1 to 10 ng·mL?1 of CEA. This amplification strategy uses an aptamer as both the recognition probe and signal probe and therefore simplifies signal transduction. Conceivably, this detection scheme may be adapted to numerous other electrochemical bioassays if respective antibodies and aptamers are available.
Graphical abstract Schematic presentation of an electrochemical aptasensor based on aptamer induced electrochemical current for the detection of cancer biomarker carcinoembryonic antigen (CEA). Gold nanorods (GNR) are chosen for the immobilization of aptamers to increase the loading of aptamers.
The authors describe four different kinds of sorbents for solid-phase extraction (SPE) and preconcentration of proteins from complex samples. All are based on the use of a poly(glycidyl-co-ethylene dimethacrylate) host monolith that was chemically functionalized by using two different ligands (ammonia and cysteamine). Gold nanoparticles (AuNPs) or silver NPs were then assembled to the amino or thiol groups. The resulting materials are shown to be viable stationary phases for use in SPE cartridges. The sorbents can selectively retain bovine serum albumin, and the thiol-modified sorbents containing AuNPs and AgNPs provide the highest recoveries (>90%) and satisfactory loading capacities (29.3 and 17.6 μg?mg?1 of sorbent, respectively). The applicability of these nanosorbents was demonstrated by preconcentrating viscotoxins from mistletoe extracts. The enriched fractions were subjected to MALDI-TOF analysis to underpin their selectivity.
Graphical abstract Hybrid materials based on methacrylate polymers modified with gold or silver nanoparticles were used as sorbents for solid phase extraction and preconcentration of bovine serum albumin and mistletoe viscotoxins, this followed by MALDI-TOF analysis.
The authors have synthesized spindle-like ZnO nanorods closely anchored to CdS nanoparticles (NPs) placed on gold NPs (ZnO-CdS@Au). It is shown that the ZnO-CdS@Au nanocomposite can serve as a photoactive material for use in photoelectrochemical (PEC) detection by efficiently absorbing light and then promoting electron transfer. A visible light-driven PEC detection platform for tetracycline (TET) was fabricated by placing the nanocomposite on an ITO and immobilizing the TET-binding aptamer as biorecognition element. PEC can be quantified by applying a bias potential of +?0.4 V (vs. SCE) and visible light irradiation. The aptamer on the electrode specifically captures the TET present in the solution to produce a restored photocurrent signal through the reaction between the captured TET and the photogenerated holes. The electrode has a linear response in the 50 to 200 nM TET concentration range, with a 4.5 nM detection limit (at an S/N ratio of 3). In our perception, this novel PEC detection strategy based on ZnO-CdS@Au nanocomposite demonstrated an ultrasensitive method for TET detection with high selectivity and good stability.
Graphical abstract Gold nanoparticles and CdS nanoparticles were deposited on the spindle-like ZnO nanorod surface (ZnO-CdS@Au). Photoelectrochemical detection of tetracycline (TET) was realized with high selectivity and good stability utilizing ZnO-CdS@Au as transducer and TET-binding aptamer as biorecognition element.
A nanocomposite prepared from reduced graphene oxide (rGO) and silver nanoparticles (AgNPs) is used in an electrochemical aptasensor for the sensitive and selective determination of the antibiotic chloramphenicol (CAP). The nanocomposite was obtained by electrostatic assembly of AgNPs on the surface of polyelectrolyte-functionalized rGO and then used to modify a glassy carbon electrode. The biosensor is then obtained by immobilizing the aptamer against CAP. When incubated with solutions of CAP, the sensor surface is loaded with CAP due to aptamer recognition. The captured CAP can be electrochemically reduced to yield a current that is strongly enhanced as a result of the excellent electrocatalysis property of the graphene/AgNP-nanocomposite. Under optimum conditions, the calibration plot is linear in the 0.01 to 35 μM concentration range, with a 2 nM detection limit (at 3σ). The sensor is reproducible, stable, selective over homologous interferents, and performs excellently when analyzing CAP in milk samples.
Graphical Abstract A graphene/silver nanoparticle-based electrochemical aptasensor is designed for the selective determination of the antibiotic chloramphenicol (CAP). The excellent electrocatalytic reduction of CAP specifically captured onto the electrode surface enables the sensitive electrochemical signal transduction of the biosensor by linear sweep voltammetry (LSV).
An aptamer based assay is described for the colorimetric detection of adenosine. The presence of adenosine triggers the deformation of hairpin DNA oligonucleotide (HP1) containing adenosine aptamer and then hybridizes another unlabeled hairpin DNA oligonucleotide (HP2). This leads to the formation of a double strand with a blunt 3′ terminal. After exonuclease III (Exo III)-assisted degradation, the guanine-rich strand (GRS) is released from HP2. Hence, the adenosine-HP1 complex is released to the solution where it can hybridize another HP2 and initiate many cycles of the digestion reaction with the assistance of Exo III. This leads to the generation of a large number of GRS strands after multiple cycles. The GRS stabilize the red AuNPs against aggregation in the presence of potassium ions. If, however, GRS forms a G-quadruplex, it loses its ability to protect gold nanoparticles (AuNPs) from salt-induced AuNP aggregation. Therefore, the color of the solution changes from red to blue which can be visually observed. This colorimetric assay has a 0.13 nM detection limit and a wide linear range that extends from 5 nM to 1 μM.
Graphical abstract Schematic presentation of a colorimetric aptamer biosensor for adenosine detection based on DNA cycling amplification and salt-induced aggregation of gold nanoparticles.
A nanocomposite consisting of cadmium oxide decorated with carbon nanotubes (CdO.CNT NC) was prepared by a wet-chemical technique, and its optical, morphological, and structural properties were characterized by FTIR, UV/Vis, FESEM coupled to XEDS, XPS, and XRD methods. A flat glassy carbon electrode was modified with the nanocomposite to obtain a sensor for L-glutathione (GSH) which displays improved sensitivity, a large dynamic range and good long-term stability. The calibration plot (best acquired at a voltage of 0.5 V) is linear (r2 = 0.99) in the 0.1 nM to 0.01 M GSH concentration range. The detection limit is as low as 30.0 pM, and the sensitivity is ~9.49 μA?μM?1?cm?2. To the best of our knowledge, this is the first report on the determination of GSH using such a modified glassy carbon electrode (GCE) in combination with I-V method. The GCE was applied to the selective determination of GSH in spiked rabbit serum samples and gave acceptable results.
Graphical abstract A selective glutathione biosensor based on wet-chemically prepared CdO.CNT/Nafion/GCE was fabricated by reliable I-V method and shows good analytical parameters such as high sensitivity, low detection limit, long-term stability, and large dynamic range.
An electrochemiluminescent (ECL) aptamer based method is described for the determination of thrombin. Three-dimensional nitrogen-doped graphene oxide (3D-NGO) was placed on a glassy carbon electrode (GCE) to provide an electrode surface that displays excellent electrical conductivity and acts as a strong emitter of ECL. The modified electrode was further coated with chitosan via electrodeposition. Finally, the amino-modified aptamer was immobilized on the modified GCE. The interaction between thrombin and aptamer results in a decrease in ECL. The assay has a linear response in the 1 fM to 1 nM thrombin concentration range and a 0.25 fM lower detection limit (at an S/N ratio of 3). The method was applied to the determination of thrombin in spiked human plasma samples, and recoveries ranged between 94 and 105% (with RSDs of <3.6%). The calibration plot was recorded at potential and wavelength of fluorescence emission (wavelength:?445 nm; potential:?0 to -2 V).
Graphical abstract A bare glassy carbon electrode (GCE) does not display electrochemiluminescence (ECL). If, however, nitrogen-doped graphene quantum dots, chitosan, and three-dimensional nitrogen-doped graphene oxide (NGQD-chitosan/3D-NGO) are electrodeposited on the GCE, strong ECL can be observed. The ECL intensity decreased after aptamer and bovine serum albumin (BSA) were dropped onto the electrode (curve a). However, the ECL further decreases after addition of thrombin (TB; curve b).
We describe the preparation of a nanohybrid consisting of nitrogen doped reduced graphene oxide and CuS nanoparticles (N-rGO/CuS) by in-situ microwave irradiation at weight ratios of 25/75, 50/50, and 75/25. The resulting nanohybrids were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, FTIR, spectroscopy, scanning electron and transmission electron microscopy, electrochemically by cyclic voltammetry and electrochemical impedance analysis. It is shown that the CuS nanoparticles are evenly decorated onto the N-rGO surface. The nanohybrids was placed on glassy carbon electrode (GCE) where they showed electro-reductive activity towards picric acid, typically at working voltages between ?0.2 and ?0.8 V (vs. SCE). Effects of pH value and scan rate were evaluated, and it is shown that two electrons are involved in electro-reduction. The detection limits of the GCE modified with various N-rGO/CuS hybrids (with 25/75, 50/50, and 75/25 wt%) are 6.2, 3.2, and 0.069 μM respectively. The method demonstrates its applicability in sensing of picric acid with good reproducibility.
Graphical abstract Nitrogen doped reduced graphene oxide nanohybrids was synthesized for the detection of picric acid. A straightforward and preconcentration free analysis of picric acid was successfully demonstrated at nanomolar levels using the nanohybrids.
Graphene oxide doped with nitrogen and sulfur was decorated with gold nanoparticles (AuNP-SN-GO) and applied as a substrate to modify a glassy carbon electrode (GCE). An aptamer against the model protein thrombin was self-assembled on the modified GCE which then was exposed to thrombin. Following aptamer-thrombin interaction, biotin-labeled DNA and aptamer 2 are immobilized on another AuNP-SN-GO hybrid and then are reacted with the thrombin/AuNP-SN-GO/GCE to form a sandwich. The enzyme label horseradish peroxidase (HRP) was then attached to the electrode by biotin–avidin interaction. HRP catalyzes the oxidation of hydroquinone by hydrogen peroxide. This generates a strong electrochemical signal that increases linearly with the logarithm of thrombin concentration in the range from 1.0?×?10?13 M to 1.0?×?10?8 M with a detection limit of 2.5?×?10?14 M (S/N?=?3). The assay is highly selective. It provides a promising strategy for signal amplification. In our perception, it has a large potential for sensitive and selective detection of analytes for which appropriate aptamers are available.
Graphic abstract A sandwich-type electrochemical aptasensor is fabricated for detection of thrombin using a glassy carbon electrode modified with nitrogen- and sulfur-doped graphene oxide and gold nanoparticles.
The authors describe a dual signal amplification strategy for improving the sensitivity of electrochemical aptasensor. Hydroxyapatite nanoparticles (HAP-NPs) serve as the support for deposition of the respective aptamer. Both the HAP-NPs and the aptamer contain phosphate groups which can react with molybdate to form a redox-active molybdophosphate precipitate on the surface of a glassy carbon electrode (GCE). On applying a relatively low voltage of 0.21 V (vs. Ag/AgCl), a current is generated whose intensity depends on the concentration of the analyte. The cancer biomarker platelet-derived growth factor BB (PDGF-BB) is chosen as a model antigen (analyte). The assay works by sequential deposition of antibody against PDGF-BB, analyte (PDGF-BB) and anti-PDGF-BB aptamer modified HAP-NPs on the GCE to form a sandwich structure. The amperometric signal is linear in the 0.1 pg.mL?1 to 10 ng.mL?1 PDGF-BB concentration range, with a detection limit as low as 50 fg.mL?1. The assay was successfully applied to the determination of PDGF-BB in serum samples. In our perception, this signal amplification strategy has a wide scope in that it can be adapted to the preparation of other aptasensors for biomarkers and related species.
Graphical abstract Schematic of an electrochemical aptasensor based on dual signal amplification strategy. It was applied to the detection of cancer biomarker platelet-derived growth factor BB (PDGF-BB). Hydroxyapatite (HAP) nanoparticles were chosen for the immobilization of aptamers to increase the loading of aptamers.
This article reports on a novel aptamer-based platform for the quantitation of urea by using an aptamer with high affinity and selectivity for urea. The surface of a glassy carbon electrode (GCE) was modified by drop casting a cocktail consisting of carbon nanotubes and reduced graphene oxide (rGO) decorated with platinum-gold nanoparticles. The urea aptamer was then immobilized on the nanocomposite via covalent conjugation. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to trace the modification of the GCE. Binding of urea caused the aptamer to be folded, and this result in an inhibition of the interfacial charge transfer rate when using hexacyanoferrate as an electrochemical redox probe. The change in redox current was quantified by differential pulse voltammetry, typically at a working voltage of 0.22 V vs. Ag/AgCl. The assay has a 1.9 pM detection limit, and the response is linear up to 150 nM concentration of urea. The superior selectivity and affinity of aptamer-modified GCE makes it a most useful tool for analysis of urea present in very low concentrations.
The article describes a colorimetric assay for the determination of thrombin. It is based on the application of a triple enzyme-mimetic activity and a dual aptamer binding strategy. The triple signal amplification relies on oxidation of the chromogenic enzyme substrate 3,3,5,5-tetramethylbenzidine (TMB) that is catalyzed by composites consisting of graphene oxide (GO), gold/platinum nanoparticles (AuPtNP), and aptamer (Apt15), a G-quadruplex/hemin conjugate. The dual-aptamer target binding strategy is based on the fact that thrombin has two active sites to be recognized by its aptamers (Apt15 and Apt29). Magnetic beads (MBs) were modified with Apt29 (Apt29-MB) and then are bound by the GO-AuPtNP-Apt15/G-quadruplex/hemin composites. In the presence of thrombin, Apt29-MB and the GO-AuPtNP-Apt15/G-quadruplex/hemin composites form a sandwich-like superstructure. Thus, the absorbance increases due to the formation of TMB oxide produced by catalysis of the composites. Under optimized conditions, the absorbance at 450 nm increases linearly in the 0.30 to 100 nM thrombin concentration range, and the limit of detection is 0.15 nM. The method is simple, rapid, and does not require complicated instrumentation. Bovine serum albumin, human serum albumin and other proteins were found not to interfere.
Graphical abstract Schematic presentation of the photometric thrombin assay based on a triple enzyme-mimetic activity of combined nanomaterials (consisting of GO, AuPtNPs and the G-quadruplex/hemin DNAzyme) and two aptamers TMB: 3,3,5,5-tetramethylbenzidine, TMBox: 3,3,5,5-tetramethylbenzidine oxide, AuPtNP: gold/platinum nanoparticles).
A novel electrochemiluminescent (ECL) method for highly sensitive detection of gene mutations was designed based on the amplification strategy of dual-functional aluminum(III). A film composed of nafion and polyaniline (Nafion-PANI) was placed onto glassy carbon electrode (GCE) in order to improve conductivity and stability, and then cadmium sulfide quantum dots (CdS QDs) were attached as an ECL label. Al(III) was introduced in order to enhance the ECL signal intensity of the CdS QDs by filling the surface electronic defects of CdS QDs. The Al(III) ions also assist by improving sensitivity by promoting the electron transfer at the GCE and by retaining plenty of single-stranded DNA (ssDNA). The ECL is generated at typically ?1.5 V in the presence of containing K2S2O8. Compared to conventional ECL based DNA biosensors, the one described here – based on the use of dually functional Al(III) ions – enables ssDNA to be detected in the 1 f. to 10 nM concentration range, with a 6 f. detection limit. This method was applied to the quantitation of target ssDNA with different mismatching status in human serum. In our perception, it represents a highly attractive tool for the detection of ssDNA and has a particular potential in the diagnosis of hereditary diseases.
Graphical abstract Preparation and schematic illustration of dual-functional aluminum(III)-based electrochemiluminescent for detection of target ssDNA.
The interference by dissolved oxygen is an obstacle in electrochemical immunoassays. The authors are reporting here on a method that employs a working potential that is below the reduction potential for oxygen and hence is not interfered by oxygen/air. Ternary Pt-Co-Cu nanodendrites were prepared by a one-pot reaction. They were placed on a glassy carbon electrode (GCE) modified with gold nanoparticles (AuNPs) where they showed excellent catalytic activity toward the reduction of hydrogen peroxide at a reduction potential of ?0.015 V (vs. SCE). Dissolved oxygen, in contrast, is not reduced at this potential. In order to obtain a sandwich-type of voltammetric immunosensor, antibody against insulin (Ab1) immobilized on the AuNPs on the GCE. The secondary antibody (Ab2) was labeled with Pt-Co-Cu nanodendrites as signal marker for signal amplification. After adding hydrogen peroxide, its catalytic oxidation by the immunosensor depends on its loading with insulin. Hence, insulin can be quantified due to the positive correlation that exists between current and the concentration of ternary Pt-Co-Cu nanodendrites on the electrode. The sensor has a linear response in the 0.2 pM to 2 nM insulin concentration range, with a 0.08 pM detection limit. The assay is well reproducible, acceptably selective, and the sensor is fairly stable over time.
Graphical abstract One-pot synthesis of ternary Pt-Co-Cu nanodendrites for oxygen interference-free electrochemical detection of insulin. GCE (glassy carbon electrode). Pt-Co-Cu NP (Pt-Co-Cu nanoparticles). BSA (bovine serum albumin). Ab1 (coating antibody). Ab2 (labeling antibody). The sandwich-type electrochemical immunosensor has been used for detecting insulin with high sensitivity, which is based on Au nanoparticles for biomolecular immobilization and the one-pot synthesis of ternary Pt-Co-Cu nanodendrites as label enhancer.
5-Hydroxymethylcytosine in DNA (5hmC-DNA) plays an important biological role in sculpting the epigenetic landscape. Its presence is linked to diseases, especially cancers. The authors describe an amperometric biosensor for the determination of 5hmC. It is based on a chemical modification of the hydroxy group of 5hmC in the DNA sequence. Enzymatic signal amplification is accomplished by using DNA methyltransferase (M.HhaI-DNA-cytosine-5-methyltransferase) to achieve chemical modification. A graphene-perylenetetracarboxylic acid nanocomposite was used to modify a glassy carbon electrode (GCE) that acts as a substrate electrode. A composite consisting of horseradish peroxidase on silica/poly(acrylic acid) brushes is employed as the signal amplification unit. Under the optimized conditions, there is a linear response to the logarithm of the 5hmC-DNA concentration in the range from 0.5 to 30 nM, with a 0.23 nM detection limit (at an S/N ratio of 3) in the potential range from ?0.3 V to -0.8 V at 100 mV/s. The bioassay has excellent specificity and can even discriminate the similar base 5mC.
Graphical abstract An amperometric biosensor is fabricated for 5-hydroxymethylcytosine (5hmC) determination, where DNA methyltransferase was used to achieve chemical modification of 5hmC, and spherical poly(acrylic acid) brushes conjugated horseradish peroxidase was used as the signal amplification unit. The biosensor showed high sensitivity and specificity.
A nanocomposite consisting of polyaniline and multiwalled carbon nanotubes was tethered with a thiolated thrombin-specific aptamer and placed on a glassy carbon electrode (GCE) to obtain a biosensor for thrombin that has a limit of detection of 80 fM. Tethering was accomplished via a thiol-ene reaction between thiolated thrombin aptamer (TTA) and oxidized polyaniline (PANI) that was chemically synthesized in the presence of solution-dispersed multiwalled carbon nanotubes (MWCNTs). The modified GCE exhibits a pair of well-defined redox peaks (at 50/?25 mV) of self-doped PANI in neutral solution, and the tethered TTA-thrombin interaction gives a decreased electrochemical signal. Cyclic voltammetry, scanning electron microscopy and ultraviolet visible spectroscopy were used to characterize the film properties. This amperometric aptasensor is sensitive, selective and reproducible. It was applied to the determination of thrombin in spiked human serum (0.2 to 4 nM) and gave recoveries that ranged from 95 to 102%.
Graphical abstract A nanocomposite consisting of polyaniline (PANI) and multiwalled carbon nanotubes (MWCNTs) was tethered with a thiolated thrombin aptamer (TTA) and placed on a glassy carbon electrode (GCE) to obtain a biosensor for thrombin that has a 80 f. detection limit.
A sensitive visual aptamer-based assay is presented for the determination of ractopamine (RAC) in animal feed beef. In the absence of RAC, the aptamer binds to gold nanoparticles (AuNPs) and this prevents the AuNPs to undergo salt-induced aggregation which usually is accompanied by a color change from red to blue. If however, RAC is present, it will bind to the aptamer while the AuNPs remain uncoated so that aggregation and a color change will occur due to salt-induced aggregation. This can be monitored by spectrophotometer or even with bare eyes. Under optimal conditions, the aptasensor exhibits a linear range that covers the 10 to 400 ng.mL￣1 RAC concentration range. The limit of detection is as low as 10 ng.mL￣1. In order to further improve selectivity, a RAC-selective molecularly imprinted membrane was prepared and used to pre-extract RAC from complex samples. The combined method (molecularly imprinted membrane and aptasensor) was applied to the determination of RAC in spiked animal feed and beef and gave recoveries that ranged from 72.7 % to 87.3 % for complete feed and from 78.2 % to 86.5 % for beef, respectively.
Graphical abstract A sensitive visual aptamer-based assay based on aggregation of gold nanoparticles in combination with a molecularly imprinted polymer was developed for the determination of ractopamine (RAC) in animal feed and beef.
The authors report that the peroxidase-like activity of Au@Pt core-shell nanohybrids (Au@PtNHs) is selectively inhibited by cysteine. This finding has led to a highly sensitive colorimetric assay for cysteine that is based on the nanohybrid-catalyzed oxidation of TMB by H2O2 to form a blue product. The method has a detection limit of 5.0 nM and a linear range from 10 nM to 20 μM. The assay is highly selective over other amino acids. It was successfully applied to the determination of cysteine in an injection containing a mixture of amino acids.
Graphical abstract The peroxidase-like activity of Au@Pt core-shell nanohybrids (Au@PtNHs) is selectively inhibited by cysteine, enabling the determination of cysteine.
