Electrochemical Nanoprobes Research Articles

An ultrasensitive sandwich-type electrochemical immunosensor based on rGO-TEPA/ZIF67@ZIF8/Au and AuPdRu for the detection of tumor markers CA72-4

Cancer antigen 72–4 (CA72-4) is an important marker of cancer detection, and accurate detection of CA72-4 is urgently required. Herein, a sandwich-type immunosensor was constructed for detection CA72-4 based on composite nanomaterial as the substrate material and trimetal nanoparticles as the nanoprobe. The composite nanomaterial rGO-TEPA/ZIF67@ZIF8/Au used as a selective bio-recognition element were modified on the glassy carbon electrode (GCE) surface. Meanwhile, the electrochemical nanoprobes were fabricated through the AuPdRu trimeric metal. After the target antigen 72–4 were captured, the nanoprobes were further assembled to form an antibody1 (Ab1)- antigen-antibody2 (Ab2) nanoprobes sandwich-like system on the electrode surface. Then, hybrid the substrate material rGO-TEPA/ZIF67@ZIF8/Au and the AuPdRu trimeric metal nanoprobes efficiently catalyzed the reduction of H2O2 and amplified the electrochemical signals. Cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and Chronoamperometry (I-T) methods were used to characterize the performance and detection capabilities for CA72-4 of the prepared immunosensors. The results showed that the detection limit was 1.8 × 10−5 U/mL (S/N = 3), and the linear range was 0.001–1000 U/mL. This study provides a new signal amplification strategy for electrochemical sensors and a theoretical basis for the clinical application of immunosensor to detect other tumor markers.

Visualizing Overall Water Splitting on Single Microcrystals of Phosphorus-Doped BiVO4 by Photo-SECM.

Particulate bismuth vanadate (BiVO4) has attracted considerable interest as a promising photo(electro)catalyst for visible-light-driven water oxidation; however, overall water splitting (OWS) has been difficult to attain because its conduction band is too positive for efficient hydrogen evolution. Using photoscanning electrochemical microscopy (photo-SECM) with a chemically modified nanotip, we visualized for the first time the OWS at a single truncated bipyramidal microcrystal of phosphorus-doped BiVO4. The tip simultaneously served as a light guide to illuminate the photocatalyst and an electrochemical nanoprobe to observe and quantitatively measure local oxygen and hydrogen fluxes. The obtained current patterns for both O2 and H2 agree well with the accumulation of photogenerated electrons and holes on {010} basal and {110} lateral facets, respectively. The developed experimental approach is an important step toward nanoelectrochemical mapping of the activity of photocatalyst particles at the subfacet level.

Photo-scanning Electrochemical Microscopy Observation of Overall Water Splitting at a Single Aluminum-Doped Strontium Titanium Oxide Microcrystal

Particulate photocatalysts for the overall water splitting (OWS) reaction offer promise as devices for hydrogen fuel generation. Even though such photocatalysts have been studied for nearly 5 decades, much of the understanding of their function is derived from observations of catalyst ensembles and macroscopic photoelectrodes. This is because the sub-micrometer size of most OWS photocatalysts makes spatially resolved measurements of their local reactivity very difficult. Here, we employ photo-scanning electrochemical microscopy (photo-SECM) to quantitatively measure hydrogen and oxygen evolution at individual OWS photocatalyst particles for the first time. Micrometer-sized Al-doped SrTiO3/Rh2-yCryO3 photocatalyst particles were immobilized on a glass substrate and interrogated with a chemically modified SECM nanotip. The tip simultaneously served as a light guide to illuminate the photocatalyst and as an electrochemical nanoprobe to observe oxygen and hydrogen fluxes from the OWS. Local O2 and H2 fluxes obtained from chopped light experiments and photo-SECM approach curves using a COMSOL Multiphysics finite-element model confirmed stoichiometric H2/O2 evolution of 9.3/4.6 μmol cm-2 h-1 with no observable lag during chopped illumination cycles. Additionally, photoelectrochemical experiments on a single microcrystal attached to a nanoelectrode tip revealed a strong light intensity dependence of the OWS reaction. These results provide the first confirmation of OWS at single micrometer-sized photocatalyst particles. The developed experimental approach is an important step toward assessing the activity of photocatalyst particles at the nanometer scale.

Detection of prostate specific antigen in whole blood by microfluidic chip integrated with dielectrophoretic separation and electrochemical sensing

The efficient detection of cancer markers has faced many challenges, such as severe interference, complicated and time-consuming operation, low sensitivity and so on. In this paper, a microfluidic chip integrated with electrodes for dielectrophoretic (DEP) separation, microchannels for electrochemical nanoprobes binding and differential pulse voltammetry (DPV) detection was proposed for the sensitive and rapid detection of prostate specific antigen (PSA) in whole blood. The functional units, which could realize cell separation, PSA derivatization (binding of electrochemical nanoprobes), capture and detection, were integrated on the microfluidic chip. The well-designed V-shaped interdigital electrode arrays provided DEP separation for blood cells with efficiency as high as 98%. Particularly, DEP effect significantly improved the sensitivity of PSA detection and reduced the detection limit by two orders of magnitude. In order to achieve sensitive detection of PSA, binding of electrochemical nanoprobes and then DPV detection was selected and integrated following the DEP separation. A sandwich structure based on electrochemical nanoprobes and dual-aptamers for on-chip DPV detection was proposed, which included self-synthesized electrochemical nanoprobes bovine serum albumin/detection aptamer 2/polythionine@gold nanoparticles (BSA/Apt2/PThi@Au NPs), target PSA, and sensing interface 6-mercaptohexanol/capture aptamer 1/gold nanoparticles on gold electrode (MCH/Apt1/Au NPs/Au). The method of quantitative detection of PSA in whole blood was then established. The excellent performance of the microfluidic chip allowed the determination of PSA in whole blood in the range of 1 pg/mL ∼10 ng/mL with an ultralow limit of detection of 0.25 pg/mL, which was better than the results obtained by conventional methods.

Synthesis of three-dimensional nickel ferrite nanospheres decorated activated graphite nanoplatelets for electrochemical detection of vortioxetine with pharmacokinetic insights in human volunteers.

An innovative electrochemical nanoprobe was developed for determination of vortioxetine (VORT), a serotonergic antidepressant drug, for the first time. The fabrication of thenanoprobe isbased on decoration of aglassy carbon electrode with three-dimensional nickel ferrite nanospheres modified activated graphite nanoplatelets (3D NiFe2O4 NS/AGNP/GCE). The morphological characterization of the nanoprobe was carried out via scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDS), N2-adsorption-desorption isotherm, and powder X-ray spectroscopy (PXRD). In addition, the electrochemical behavior of the nanoprobe was described usingcyclic voltammetry (CV), differential pulse voltammetry(DPV), and electrochemical impedance spectroscopy (EIS). A well-defined and irreversible peak at 0.82V was seen at the surface of 3D NiFe2O4 NS/AGNP/GCE. The proposed nanoprobe exhibited outstanding electro-catalytic activity towards VORT oxidation. Under the optimized conditions, the anodic oxidation currents were linearly proportional to VORT concentration at the working range 1.8-90nM with aLOD of 0.55nM. The nanoprobe was used to determine VORT in pharmaceutical tablets and human plasma samples. Satisfactory recoveries and RSD percentages were obtained in the range 103.8-107.7% (RSD% = 2.7-3.1%) and 101.4-105.3% (RSD % = 2.8-3.4%) for tablets and plasma samples, respectively. Moreover, the method was used to monitor VORT during apharmacokinetic study in human volunteers with satisfactory results. The 3D NiFe2O4 NS/AGNP/GCE shows excellent sensitivity, reproducibility, and selectivity towards VORT detection. The proposed electrode could be utilized as simple, rapid, and inexpensive sensing tool for routine analysis and during pharmacokinetic/pharmacodynamic investigations. Graphical abstract.

Lanthanum cobaltite supported on graphene nanosheets for non-enzymatic electrochemical determination of catechol.

An electrochemical sensor isdescribed for the determination of catechol (CT) based on the nanocomposite of lanthanum cobaltite supported on graphene nanosheets (LaCo/GNS). The nanocomposite was systematically examined by various analytical and spectroscopic methods. The LaCo/GNS-modified electrode exhibites good electrochemical activity towards CT determination compared to other modified and unmodified electrodes. The electrochemical signal was acquired at a redox potential of 0.21 (Epa) and 0.17 (Epc) Volt (vs. Ag/AgCl). Theproposed electrode exhibits low detection limit (1.0nM), wide working range (0.009-132μM), and good sensitivity (5.68μAμM-1cm-2). The electrochemical nanoprobe has good selectivity over potentially interfering compounds. Theelectrochemical sensor was applied to the analysisof environmental samples with acceptable recovery. Graphical abstractSchematic representation of electrochemical determination of catechol in the environmental sample analysis using lanthanum cobaltite supported on graphene nanosheets.

Facile fabrication of a novel 3D rose like lanthanum doped zirconia decorated reduced graphene oxide nanosheets: An efficient electro-catalyst for electrochemical reduction of futuristic anti-cancer drug salinomycin during pharmacokinetic study

An innovative electrochemical nanoprobe, for analysis of salinomycin (SAL), was proposed. The nanoprobe based on decoration of glassy carbon electrode (GCE) with 3D rose like La3+@ ZrO2 supported on reduced graphene oxide (RGO) nanosheets. The 3D rose like La3+@ ZrO2 was synthesized via sintering process. The successful decoration of 3D rose like La3+@ ZrO2 on the surface of RGO was characterized using different spectroscopic and analytical techniques. The obtained voltammetric results confirmed the good electrochemical performance of 3D rose like La3+@ ZrO2 in terms of lower peak potential (Epc) and higher cathodic current (Ipc). Moreover, the modified nanoprobe showed wide linearity range (0.34–115 × 10−8 M), lower detection limit (0.11 × 10−8 M) and higher selectivity. Besides, the nanocomposite showed good applicability for analysis of SAL in biological fluids and during pharmacokinetic evaluation in rabbit plasma. The obtained results opens a new venue for the determination of futuristic drug, SAL, during pharmacokinetic and pharmacodynamics studies.

Efficient AuPd@GO-based electrochemical nanoprobe for sensitive detection of histone acetylase activity and its inhibitor.

Histone acetylase (HAT p300), which has aroused great concern in fundamental research and clinical applications, serves as one class of significant tumor markers. In our work, a sensitive electrochemical immunoassay for testing HAT p300 based on both graphene-assisted supported AuPd nanomaterial (AuPd@GO composite) and a typical amperometric i-t technique with fast response is developed favorably. The AuPd@GO-based sensing mechanisms are distributed as follows: the HAT p300 derived acetylation reaction occurs at the customized peptide-immobilized electrode; the AuPd@GO composite acts as carrier to immobilize acetyl antibody, thus constructing a sandwich-type electrochemical immunosensor via an antigen and antibody interaction; importantly, a distinct electrochemical signal could be caught due to the AuPd@GO nanomaterial with a favorable electrocatalytic property to the commercialized 3,3,5',5'-tetramethyl benzidine solution (TMB). Taking advantage of AuPd@GO composite, the established immunosensor displays a wide linear range from 1pM to 1000nM, and the detection limit is 0.5pM (S/N = 3) for HAT p300. Next, the biosensor is also used to analyze the inhibitor of HAT p300 successfully, which is promising for promoting the development of electrochemical HAT-related biodetection and drug discovery. Graphical abstract A sensitive electrochemical immunoassay for testing HAT p300 based on both graphene-assisted supported AuPd nanomaterial (AuPd@GO composite) and a typical amperometric i-t technique with fast response is developed favorably.

Sputtering enhanced peroxidase like activity of a dendritic nanochip for amperometric determination of hydrogen peroxide in blood samples.

A nonenzymatic electrochemical nanoprobe is described for the fast determination of hydrogen peroxide (H2O2). A sputtered indium tin oxide electrode with a nano-hierarchical 3D gold structure is used. The nanoprobe was characterized by SEM, EDX, TEM, SAED, and electrochemical techniques. Figures of merit include (a) a fast response time (≤ 1.0s), (b) two linear dynamic ranges that extend from 10-12M to 10-10M and from 10-10M to10-5 M; and (c) a low limit of detection of 9.8 × 10-13M. The nanoprobe works in the clinical range and was applied for trace analysis of H2O2 in spiked blood samples, and recoveries ranged between 90 and 96%. It has negligible response (p< 0.001, for n= 3) toward glucose, citric acid, ascorbic acid, uric acid, glycine, and alanine. The shelf-lifetime is found to be 12weeks. Graphical abstract Schematic representation of a dendritic nanochip with peroxidase-like activity. It is made from an indium tin oxide electrode with a nanohierarchical gold structure and was used for amperometric determination of hydrogen peroxide.

Photodynamic therapy of melanoma by blue-light photoactivation of flavin mononucleotide

Melanoma is one of the most aggressive and lethal form of cancer. Photodynamic therapy (PDT) is a clinically approved technique for cancer treatment, including non-melanoma skin cancer. However, the most of conventional photosensitizers are of low efficacy against melanoma due to the possible dark toxicity at high drug concentrations, melanin pigmentation, and induction of anti-oxidant defense mechanisms. In the current research we propose non-toxic flavin mononucleotide (FMN), which is a water-soluble form of riboflavin (vitamin B2) as a promising agent for photodynamic therapy of melanoma. We demonstrated selective accumulation of FMN in melanoma cells in vivo and in vitro in comparison with keratinocytes and fibroblasts. Blue light irradiation with dose 5 J/cm2 of melanoma cells pre-incubated with FMN led to cell death through apoptosis. Thus, the IC50 values of human melanoma A375, Mel IL, and Mel Z cells were in a range of FMN concentration 10–30 µM that can be achieved in tumor tissue under systemic administration. The efficiency of reactive oxygen species (ROS) generation under FMN blue light irradiation was measured in single melanoma cells by a label-free technique using an electrochemical nanoprobe in a real-time control manner. Melanoma xenograft regression in mice was observed as a result of intravenous injection of FMN followed by blue-light irradiation of tumor site. The inhibition of tumor growth was 85–90% within 50 days after PDT treatment.

Electrochemical nanoprobe-based immunosensor for deoxynivalenol mycotoxin residues analysis in wheat samples.

Deoxynivalenol (DON) is a toxic secondary metabolite produced by several species of Fusarium fungi, which can be predominantly found in agricultural crops such as wheat. In livestock, deoxynivalenol-contaminated grain can produce vomiting, feed refusal, weight loss, and diarrhea. This paper reports an electrochemical immunosensor for the detection of residual DON mycotoxin in food samples. The device uses electrochemical nanoprobes (CdSNP-AbDON) and antigen biofunctionalized magnetic μ-particles (DON-BSAMP) to detect the mycotoxin. CdSNP-AbDON are prepared by labelling the DON-specific antibodies with CdS nanoparticles (CdSNPs). Nanoparticle size and CdSNP-AbDON conjugation ratio are characterized using TEM images. The metal ions released by the CdSNP are reduced at the working electrode and read by anodic stripping voltammetry. DON can be detected in PBST buffer with an IC50 of 6.74 ± 0.19μgL-1. The high detectability of the immunosensor developed allows detection of DON residues in 50-fold diluted wheat extracts. The limit of detection (LOD, IC90) accomplished in wheat is of 342.4μgkg-1, which is below the maximum residue limit (MRL, 1750μgkg-1 for unprocessed durum wheat, 750μgkg-1 for cereals intended for direct human consumption) established by the EU for this mycotoxin. The working range is in the interval between 610 and 6210μgkg-1. The performance of the immunosensor was compared with the ELISA assay. DON naturally contaminated wheat samples were analyzed with the immunosensor, showing acceptable recoveries. Graphical abstract.

Voltammetric aptamer based detection of HepG2 tumor cells by using an indium tin oxide electrode array and multifunctional nanoprobes

The authors describe a method for the detection and determination of human liver cancer cells in blood. The cytosensing system consists of a microfabricated chip-based electrochemical aptasensor that contains multifunctional hybrid electrochemical nanoprobes and an indium tin oxide (ITO) electrode array interface functionalized with cell-targeting aptamer and gold nanoparticles (AuNPs). The thiolated cell targeting aptamer (referred to as TLS11a) was immobilized on the ITO electrode/AuNPs for specific adhesion of hepatocellular carcinoma cells (HepG2). The hybrid nanoprobe system consists of hydroquinone (HQ) as an electrochemical probe, horseradish peroxidase (HRP), and an aptamer/hemin/G-quadruplex aggregate that was immobilized on gold/palladium-functionalized ZnO nanorods (ZnO@Au-Pd). The nanoprobes are capable of amplifying the voltammetric signal and capturing the target cells. Best operated at around −90 mV (vs Ag/AgCl), the electrode has a linear response that covers the 10^2 to 10^7 HepG2 cells per mL concentration range, with a 10 cell per mL detection limit. Captured cells may be released from the electrode via electrochemical desorption to break the Au-S bonds.

Sensitive electrochemical aptamer cytosensor for highly specific detection of cancer cells based on the hybrid nanoelectrocatalysts and enzyme for signal amplification.

Human cancer is becoming a leading cause of death in the world and the development of a straightforward strategy for early detection of cancer is urgently required. Herein, a sandwich-type electrochemical aptamer cytosensor was developed for detection of human liver hepatocellular carcinoma cells (HepG2) based on the hybrid nanoelectrocatalysts and enzyme for signal amplification. The thiolated TLS11a aptamers were used as a selective bio-recognition element, attached to the gold nanoparticles (AuNPs) modified the glassy carbon electrode (GCE) surface. Meanwhile, the electrochemical nanoprobes were fabricated through the G-quadruplex/hemin/aptamer complexes and horseradish peroxidase (HRP) immobilized on the surfaces of Au@Pd core-shell nanoparticle-modified magnetic Fe3O4/MnO2 beads (Fe3O4/MnO2/Au@Pd). After the target cells were captured, the hybrid nanoprobes were further assembled to form an aptamer-cell-nanoprobes sandwich-like system on the electrode surface. Then, hybrid Fe3O4/MnO2/Au@Pd nanoelectrocatalysts, G-quadruplex/hemin HRP-mimicking DNAzymes and the natural HRP enzyme efficiently catalyzed the oxidation of hydroquinone (HQ) with H2O2, amplifying the electrochemical signals and improving the detection sensitivity. This electrochemical cytosensor delivered a wide detection range of 1×10(2)-1×10(7)cellsmL(-1), high sensitivity with a low detection limit of 15cellsmL(-1), good selectivity and repeatability. Finally, an electrochemical reductive desorption method was performed to break gold-thiol bond and desorb the components on the AuNPs/GCE for regenerating the cytosensor. These results have demonstrated that the electrochemical cytosensor has the potential to be a feasible tool for cost-effective cancer cell detection in early cancer diagnosis.

Electrochemical nanoprobes for the chemical detection of neurotransmitters.

Neurotransmitters, acting as chemical messengers, play an important role in neurotransmission, which governs many functional aspects of nervous system activity. Electrochemical probes have proven a very useful technique to study neurotransmission, especially to quantify and qualify neurotransmitters. With the emerging interests in probing neurotransmission at the level of single cells, single vesicles, as well as single synapses, probes that enable detection of neurotransmitters at the nanometer scale become vitally important. Electrochemical nanoprobes have been successfully employed in nanometer spatial resolution imaging of single nanopores of Si membrane and single Au nanoparticles, providing both topographical and chemical information, thus holding great promise for nanometer spatial study of neurotransmission. Here we present the current state of electrochemical nanoprobes for chemical detection of neurotransmitters, focusing on two types of nanoelectrodes, i.e. carbon nanoelectrode and nano-ITIES pipet electrode.

Gelsolin bound β-amyloid peptides(1–40/1–42): Electrochemical evaluation of levels of soluble peptide associated with Alzheimer's disease

A method for the highly sensitive determination of soluable β-amyloid peptides (Aβ1–40/1–42) that employs a detection bioconjugate of HRP–Au–gelsolin as the electrochemical nanoprobe is presented. Contrary to previous detection notions that utilized antibodies, which could specifically recognize the N- or C-terminus of peptides, we demonstrate herein that the reported specific binding between gelsolin and Aβ might provide an alternative way to evaluate the peptides sensitively and selectively. The HRP–Au–gelsolin nanohybrid was designed by one-pot functionalization of Au nanaoparticles (NPs) with horseradish peroxidase (HRP) and gelsolin. Through a sandwich-type sensor array, soluble Aβ1–40/1–42 were captured onto the array due to the interactions between targeted peptides and surface-confined gelsolin and electrochemical signals were amplified by abundant attachments of HRP labeled on AuNPs, which could specifically catalyse its substrate, 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 to give rise to measurable signals. The proposed gelsolin-bound Aβ methodology displayed satisfactory sensitivity and wide linear range towards Aβ1–40/1–42 with a detection limit down to 28pM, which are verified to be sensitive-enough for the assessment of Aβ levels both in normal and Alzheimer's disease (AD) rat brains. Experimental results indicated that compared with normal group, soluble β-amyloid peptide levels in cerebrospinal fluid (CSF) and targeted brain tissues of AD rats all declined with differentiable degrees. In short, the newly unfolding strategy presents valuable information related to pathological events in brain and will exhibit a braw perspective for the early diagnosis of AD process.

Coulombimetric immunosensor for paraquat based on electrochemical nanoprobes

A new electrochemical immunosensor has been developed to detect paraquat (PQ) pesticide residues in food samples. The immunosensor presented uses electrochemical nanoprobes prepared by labeling the PQ specific antibodies with CdS nanoparticles (CdSNP) and antigen biofunctionalized magnetic μ-particles. Electrochemical measurements are performed using graphite composite electrodes (GECs). After the immunochemical reaction, the CdSNP are dissolved and the metal ions released are reduced at the electrode and read in the form of current or charge signal, by the well-known anodic stripping technique. Due to the amplification effect produced by the CdSNP on the amperometric/coulombimetric signal, a very high detectability is reached. Thus, PQ can be detected with an IC50current of 0.18±0.31μgL−1 (in PBST). The immunosensor has been implemented in analyzing PQ residues in potato samples. Combined with a suitable extraction procedure PQ can be detected with a LOD current of 1.4μgkg−1, far below the maximum residue limit (MRL, 20μgkg−1) established by the EU for this pesticide in most crops. Likewise, the working range was in the interval between 3.08 and 67.76μgkg−1. Preliminary experiments demonstrate that the immunosensor presented here could be used as screening tool to distinguish between compliant and non-compliant food samples.

Multiplex acute leukemia cytosensing using multifunctional hybrid electrochemical nanoprobes at a hierarchically nanoarchitectured electrode interface

We have developed a robust, nanobiotechnology-based electrochemical cytosensing approach with high sensitivity, selectivity, and reproducibility toward the simultaneous multiplex detection and classification of both acute myeloid leukemia and acute lymphocytic leukemia cells. The construction of the electrochemical cytosensor involves the hierarchical assembly of dual aptamer-functionalized, multilayered graphene-Au nanoparticle electrode interface and the utilization of hybrid electrochemical nanoprobes co-functionalized with redox tags, horseradish peroxidase, and cell-targeting nucleic acid aptamers. The hybrid nanoprobes are multifunctional, capable of specifically targeting the cells of interest, amplifying the electrochemical signals, and generating distinguishable signals for multiplex cytosensing. The as-assembled electrode interface not only greatly facilitates the interfacial electron transfer process due to its high conductivity and surface area but also exhibits excellent biocompatibility and specificity for cell recognition and adhesion. A superstructured sandwich-type sensor geometry is adopted for electrochemical cytosensing, with the cells of interest sandwiched between the nanoprobes and the electrode interface. Such an electrochemical sensing strategy allows for ultrasensitive, multiplex acute leukemia cytosensing with a detection limit as low as ~350 cells per mL and a wide linear response range from 5 × 10(2) to 1 × 10(7) cells per mL for HL-60 and CEM cells, with minimal cross-reactivity and interference from non-targeting cells. This electrochemical cytosensing approach holds great promise as a new point-of-care diagnostic tool for early detection and classification of human acute leukemia and may be readily expanded to multiplex cytosensing of other cancer cells.

Development of a Coulombimetric immunosensor based on specific antibodies labeled with CdS nanoparticles for sulfonamide antibiotic residues analysis and its application to honey samples

A new electrochemical immunosensor has been developed to detect sulfonamide antibiotic residues in food samples. The immunosensor presented uses immunoreagents specifically developed for the broad recognition of the sulfonamide antibiotic family, a graphite composite electrode (GEC), biofunctionalized magnetic μ-particles and electrochemical nanoprobes prepared by labeling the specific antibodies with CdS nanoparticles (CdSNP). After the immunochemical reaction, the CdSNP are dissolved and the metal ions released are reduced at the electrode and read as in the form of current or charge signal, by the well-known anodic stripping technique. Due to the amplification effect on the amperometric/coulombimetric signal produced by the CdSNP, a high detectability can be reached. Thus, sulfapyridine (SPY), one of the most widely used sulfonamide congeners, can be detected in buffer with an IC50current of 0.20±0.25μgL−1. The immunosensor has been applied to the analysis of residues of this antibiotic in honey samples. Due to the reported formation of sulfonamide–sugar conjugates in this type of matrix, honey samples are first hydrolyzed in acidic media. The use of magnetic particles minimizes the matrix effect allowing to reach a detectability (LOD, limit of detection) of 0.11μgkg−1 (current measurements), far below the limits established in some countries for these types of residues in honey samples. Due to the use of magnetic racks, multiple samples can be run simultaneously. The whole analysis process can be performed in around 22min.

Polymeric microfabricated electrochemical nanoprobe with addressable electrodes

We present a polymeric microfabricated electrochemical nanoprobe (MEN) with nanometer-scale electrodes fabricated using standard photolithography. The probe and the electrodes are formed by embedding nanometer-thick metal lines between two layers of UV curable adhesive polymers, followed by dicing and detaching the MENs from the substrate. The cutting plane obtained after dicing constitutes the tip of the MENs. The thicknesses of the spin-coated polymer and of the deposited metal determine the thickness of the probe and the electrodes, respectively, and can be precisely controlled. Several polymers were characterized, including SU-8 and photosensitive polyurethanes which were found to be optimal. MENs with two and four electrodes were fabricated. The MENs were characterized by cyclic voltammetry. The reproducibility of the MENs for electrochemical measurements was optimized and the sensitivity was significantly enhanced by the controlled electrodeposition of palladium nanocrystals yielding a greater active electrode area. These MENs may be functionalized and used to analyse the concentration of chemicals by placing the MEN above them.

Probing Charge Transfer at Surfaces Using Graphene Transistors

Graphene field effect transistors (FETs) are extremely sensitive to gas exposure. Charge transfer doping of graphene FETs by atmospheric gas is ubiquitous but not yet understood. We have used graphene FETs to probe minute changes in electrochemical potential during high-purity gas exposure experiments. Our study shows quantitatively that electrochemistry involving adsorbed water, graphene, and the substrate is responsible for doping. We not only identify the water/oxygen redox couple as the underlying mechanism but also capture the kinetics of this reaction. The graphene FET is highlighted here as an extremely sensitive potentiometer for probing electrochemical reactions at interfaces, arising from the unique density of states of graphene. This work establishes a fundamental basis on which new electrochemical nanoprobes and gas sensors can be developed with graphene.