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Abstract: Paper based colorimetric biosensing platform utilizing cross-linked siloxane 3-aminopropyltriethoxysilane (APTMS) as probe was developed for the detection of a broad range of targets including H2O2, glucose and protein biomarker. APTMS was extensively used for the modification of filter papers to develop paper based analytical devices. We discovered when APTMS was cross-linked with glutaraldehyde (GA), the resulting complex (APTMS–GA) displays brick-red color, and a visual color change was observed when the complex reacted with H2O2. By integrating the APTMS–GA complex with filter paper, the modified paper enables quantitative detection of H2O2 through the monitoring of the color intensity change of the paper via software Image J. Then, with the immobilization of glucose oxidase (GOx) onto the modified paper, glucose can be detected through the detection of enzymatically generated H2O2. For protein biomarker prostate specific antigen (PSA) assay, we immobilized capture, not captured anti-PSA antibody (Ab1) onto the paper surface and using GOx modified gold nanorod (GNR) as detection anti-PSA antibody (Ab2) label. The detection of PSA was also achieved via the liberated H2O2 when the GOx label reacted with glucose. The results demonstrated the possibility of this paper based sensor for the detection of different analytes with wide linear range. The low cost and simplicity of this paper based sensor could be developed for “point-of-care” analysis and find wide application in different areas. [Copyright &y& Elsevier]

Highlights: [•] Electrical percolation is based on electrical connectivity in randomly oriented systems of discrete elements. [•] Biological semiconductor is a multi-layer 3-D carbon nanotube-antibody network with a biological ligand. [•] Molecular interactions disrupt the network continuity causing increased resistance of the network. [•] We demonstrated real time continuous detection of staphylococcal enterotoxin B at concentrations of 1ng/ml. [•] This new direct measurement biosensor has potential for multi-target real time detection. [ABSTRACT FROM AUTHOR]

Abstract: There is a well-recognized need for low cost biodetection technologies for resource-poor settings with minimal medical infrastructure. Lab-on-a-chip (LOC) technology has the ability to perform biological assays in such settings. The aim of this work is to develop a low cost, high-throughput detection system for the analysis of 96 samples simultaneously outside the laboratory setting. To achieve this aim, several biosensing elements were combined: a syringe operated ELISA lab-on-a-chip (ELISA-LOC) which integrates fluid delivery system into a miniature 96-well plate; a simplified non-enzymatic reporter and detection approach using a gold nanoparticle–antibody conjugate as a secondary antibody and silver enhancement of the visual signal; and carbon nanotubes (CNT) to increase primary antibody immobilization and improve assay sensitivity. Combined, these elements obviate the need for an ELISA washer, electrical power for operation and a sophisticated detector. We demonstrate the use of the device for detection of Staphylococcal enterotoxin B, a major foodborne toxin using three modes of detection, visual detection, CCD camera and document scanner. With visual detection or using a document scanner to measure the signal, the limit of detection (LOD) was 0.5ng/ml. In addition to visual detection, for precise quantitation of signal using densitometry and a CCD camera, the LOD was 0.1ng/ml for the CCD analysis and 0.5ng/ml for the document scanner. The observed sensitivity is in the same range as laboratory-based ELISA testing. The point of care device can analyze 96 samples simultaneously, permitting high throughput diagnostics in the field and in resource poor areas without ready access to laboratory facilities or electricity. [Copyright &y& Elsevier]

Abstract: An ultrasensitive electrochemical immunosensor based on graphene sheet (GS) has been developed. GS was used to immobilize mediator thionine (TH), horseradish peroxidase (HRP) and secondary anti-prostate-specific antigen (PSA) antibody (Ab2) and the resulting nanostructure (GS-TH-HRP-Ab2) was used as the label for the immunosensor. With primary anti-PSA antibody (Ab1) also immobilized onto the GS, the immunosensor displayed a wide range of linear response (0.002–10ng/mL), low detection limit (1pg/mL), good reproducibility, selectivity and stability. The good performance of the immunosensor is attributed to the graphene sheet''s high surface-to-volume ratio which allows the immobilization of a high-level of Ab1, Ab2, TH and HRP and its good electrical conductivity which can improve the electron transfer among TH, HRP, H2O2 and electrode. The immunosensor was used to detect the PSA contents in serum samples from patients and satisfactory test results were obtained in comparison with the ELISA test results. Thus, graphene-based labels may provide many potential applications for the detection of different cancer biomarkers. [Copyright &y& Elsevier]

Abstract: Electrical percolation-based biosensing is a new technology. This is the first report of an electrical percolation-based biosensor for real-time detection. The label-free biosensor is based on electrical percolation through a single-walled carbon nanotubes (SWNTs)–antibody complex that forms a network functioning as a “Biological Semiconductor” (BSC). The conductivity of a BSC is directly related to the number of contacts facilitated by the antibody–antigen “connectors” within the SWNT network. BSCs are fabricated by immobilizing a pre-functionalized SWNTs–antibody complex directly on a poly(methyl methacrylate) (PMMA) and polycarbonate (PC) surface. Each BSC is connected via silver electrodes to a computerized ohmmeter, thereby enabling a continuous electronic measurement of molecular interactions (e.g. antibody–antigen binding) via the change in resistance. Using anti-staphylococcal enterotoxin B (SEB) IgG to functionalize the BSC, we demonstrate that the biosensor was able to detect SEB at concentrations as low as 5ng/mL at a signal to baseline (S/B) ratio of 2. Such measurements were performed on the chip in wet conditions. The actuation of the chip by SEB is immediate, permitting real-time signal measurements. In addition to this “direct” label-free detection mode, a secondary antibody can be used to “label” the target molecule bound to the BSC in a manner analogous to an immunological sandwich “indirect” detection-type assay. Although a secondary antibody is not needed for direct detection, the indirect mode of detection may be useful as an additional measurement to verify or amplify signals from direct detection in clinical, food safety and other critical assays. The BSC was used to measure SEB both in buffer and in milk, a complex matrix, demonstrating the potential of electrical percolation-based biosensors for real-time label-free multi-analyte detection in clinical and complex samples. Assembly of BSCs is simple enough that multiple sensors can be fabricated on the same chip, thereby creating “Biological Central Processing Units (BCPUs)” capable of parallel processing and sorting out information on multiple analytes simultaneously which may be used for complex analysis and for point of care diagnostics. [Copyright &y& Elsevier]

Abstract: Staphylococcal enterotoxins (SEs) are major cause of foodborne diseases, so sensitive detection (<1 ng/ml) methods are needed for SE detection in food. The surface area, geometric and physical properties of gold nanoparticles make them well-suited for enhancing interactions with biological molecules in assays. To take advantage of the properties of gold nanoparticles for immunodetection, we have developed a gold nanoparticle-based enhanced chemiluminescence (ECL) immunosensor for detection of Staphylococcal Enterotoxin B (SEB) in food. Anti-SEB primary antibodies were immobilized onto a gold nanoparticle surface through physical adsorption and then the antibody–gold nanoparticle mixture was immobilized onto a polycarbonate surface. SEB was detected by a “sandwich-type” ELISA assay on the polycarbonate surface with a secondary antibody and ECL detection. The signal from ECL was read using a point-of-care detector based on a cooled charge-coupled device (CCD) sensor or a plate reader. The system was used to test for SEB in buffer and various foods (mushrooms, tomatoes, and baby food meat). The limit of detection was found to be ~0.01 ng/mL, which is ~10 times more sensitive than traditional ELISA. The gold nanoparticles were relatively easy to use for antibody immobilization because of their physical adsorption mechanism; no other reagents were required for immobilization. The use of our simple and inexpensive detector combined with the gold nanoparticle-based ECL method described here is adaptable to simplify and increase sensitivity of any immunological assay and for point-of-care diagnostics. [Copyright &y& Elsevier]

Abstract: A label-free immunosensor for the sensitive detection of human immunoglobulin G (IgG) was prepared based on gold nanoparticle–silver enhancement detection with a simple charge-coupled device (CCD) detector. The gold nanoparticles, which were used as nuclei for the deposit of metallic silver and also for the adsorption of antibodies, were immobilized into wells of a 9-well chip. With the addition of silver enhancement buffer, metallic silver will deposit onto gold nanoparticles, causing darkness that can be optically measured by the CCD camera and quantified using ImageJ software. When antibody was immobilized onto the gold nanoparticles and antigen was captured, the formed immunocomplex resulted in a decrease of the darkness and the intensity of the darkness was in line with IgG concentrations from 0.05 to 10ng/ml. The CCD detector is simple and portable, and the reported method has many desirable merits such as sensitivity and accuracy, making it a promising technique for protein detection. [Copyright &y& Elsevier]

Abstract: Staphylococcal enterotoxins (SEs) are a major cause of food-borne diseases, traditionally SEs assayed immunologically with ELISA. Carbon nanotubes'' (CNT) unique mechanical and electronic properties combined with a large specific surface area make them attractive for biosensing. To investigate whether CNT could improve the sensitivity of ELISA assays, we developed an optical CNT immunosensor for the detection of Staphylococcal Enterotoxin B (SEB) in food. Anti-SEB antibodies were immobilized onto a CNT surface through electrostatic adsorption and then the antibody–nanotube mixture was bound onto a polycarbonate film. SEB was then detected by a “sandwich-type” ELISA assay on the polycarbonate film. The use of CNT increased the sensitivity of the immunosensor by at least 6-fold, lowering the detection limit of SEB. The CNT immunosensor was also able to detect SEB various foods, suggesting the utility of CNT for this and other optical-based immunological detection methods. [Copyright &y& Elsevier]

Abstract: Platinum nanoparticles (PtNPs) were prepared by seed-mediated growth method with Au nanoparticles (AuNPs) playing the role of seeds. Carbon nanotubes (CNTs) and AuNPs were first dropped onto the surface of glassy carbon (GC) electrode, and then the electrode was immersed into growth solution which contains H2PtCl6 and ascorbic acid. PtNPs were successfully grown onto the CNT surface due to the chemical reduction of Pt(IV). The electrode modified with AuNPseed/PtNP/CNT film displayed excellent electrochemical response to H2O2 at 0.45V versus saturated calomel electrode (SCE) with sensitivity much larger than that of PtNP/CNT and AuNPseed/PtNP modified electrodes. Glucose oxidase was selected as a model enzyme and electrodeposited onto the AuNPseed/PtNP/CNT modified electrode in the presence of a detergent. The resulting biosensor enabled selective determination of glucose with high sensitivity of 4.49μAmM−1, quick response time about 2s, low-detection limit of 0.5μM and wide linear range from 1μM to 4mM with a correlation coefficient 0.9998. Thus, the modified electrode proved to be a nice electrochemical biosensing platform for the fabrication of oxidase-based biosensors. [Copyright &y& Elsevier]

Abstract: Gold nanowires were prepared by an electrodeposition strategy using nanopore polycarbonate (PC) membrane, with the average diameter of the nanowires about 250 nm and length about 10 μm. The nanowires prepared were dispersed into chitosan (CHIT) solution and stably immobilized onto glassy carbon electrode (GCE) surface. The electrochemical behavior of gold nanowire modified electrode and its application to the electrocatalytic reduction of hydrogen peroxide (H2O2) were investigated. The modified electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. Moreover, the good biocompatibility of nanometer-sized gold, the vast surface area of the nanowire-structure make it ideal for adsorption of enzymes for the fabrication of biosensors. Glucose oxidase was adsorbed onto the nanowire surface to fabricate glucose biosensor as an application example. The detection of glucose was performed in phosphate buffer (pH 6.98) at −0.2 V. The resulting glucose biosensor exhibited sensitive response, with a short response time (<8 s), a linear range of 10−5–2×10−2 M and detection limit of 5×10−6 M. [Copyright &y& Elsevier]

Abstract: Poly (neutral red) nanowires (PNRNWs) have been synthesized for the first time by the method of cyclic voltammetric electrodeposition using porous anodic aluminum oxide (AAO) template and were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Moreover, horseradish peroxidase (HRP) was encapsulated in situ in PNRNWs (denoted as PNRNWs–HRP) by electrochemical copolymerization for potential biosensor applications. The PNRNWs showed excellent efficiency of electron transfer between the HRP and the glassy carbon (GC) electrode for the reduction of H2O2 and the PNRNWs–HRP modified GC electrode showed to be excellent amperometric sensors for H2O2 at −0.1V with a linear response range of 1μM to 8mM with a correlation coefficient of 0.996. The detection limit (S/N =3) and the response time were determined to be 1μM and <5s and the high sensitivity is up to 318μAmM−1 cm−2. [Copyright &y& Elsevier]

Platinum nanowires (PtNW) were prepared by an electrodeposition strategy using nanopore alumina template. The nanowires prepared were dispersed in chitosan (CHIT) solution and stably immobilized onto the surface of glassy carbon electrode (GCE). The electrochemical behavior of PtNW-modified electrode and its application to the electrocatalytic reduction of hydrogen peroxide (H2O2) are investigated. The modified electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. As an application example, the glucose oxidase was immobilized onto the surface of PtNW-modified electrode through cross-linking by glutaric dialdehyde. The detection of glucose was performed in phosphate buffer at -0.2 V. The resulting glucose biosensor exhibited a short response time (<8 s), with a linear range of 10-5-10-2 M and detection limit of 5×10-6 M. [ABSTRACT FROM AUTHOR]

Abstract: Platinum nanowires (PtNWs) prepared by electrodeposition method with the help of porous anodic aluminum oxide (AAO) templates have been solubilized in chitosan (CHIT) together with carbon nantubes (CNTs) to form a PtNW–CNT–CHIT organic–inorganic system. The resulting PtNW–CNT–CHIT material brings capabilities for utilizing synergic action of PtNWs and CNTs to facilitate electron-transfer process in electrochemical sensor design. The PtNW–CNT–CHIT film modified electrode offered a significant decrease in the overvoltage for the hydrogen peroxide and showed to be excellent amperometric sensors for hydrogen peroxide at −0.1V over a wide range of concentrations, and the sensitivity is 260μAmM−1 cm−2. As an application example, by linking glucose oxidase (GOx), an amplified biosensor toward glucose was prepared. The glucose biosensor exhibits a selective determination of glucose at −0.1V with a linear response range of 5×10−6 to 1.5×10−2 M with a correlation coefficient of 0.997, and response time <10s. The high sensitivity of the glucose biosensor is up to 30μAmM−1 cm−2 and the detection limit was 3μM. The biosensor displays rapid response and expanded linear response range, and excellent repeatability and stability. [Copyright &y& Elsevier]

Abstract: Platinum nanowire arrays can be grown by electrodeposition in polycarbonate membrane, with the average diameter of the nanowires about 250nm and the height about 2μm. The nanowire array prepared by the proposed method can be considered as nanoelectrode array (NEA) with nanoelectrode density of 5×108 cm−2. While the NEA can improve the signal-to-noise ratio and decrease the detection limit, the high surface area of the platinum NEA circumvents the problem of conventional platinum electrodes associated with the limited electroactive site. The platinum NEA can direct response to hydrogen peroxide at low potential of 0V with wide linear range (1×10−7–6×10−2 m) and sensitivity 50 times larger than that of the conventional platinum electrode. With the absorption of glucose oxidase onto the ordered NEA surface, the spatially patterned glucose oxidase improves greatly the resulting biosensor. The biosensor can achieve interference free determination of glucose with wide linear range (10−6–3×10−2 m). The sensitivity of the glucose biosensor is one-fifth of the sensitivity toward hydrogen peroxide, indicating high efficiency of signal transduction. The biosensor was used to determine glucose in real blood samples, and the glucose contents determined by the present biosensor were in agreement with the results of existing method. [Copyright &y& Elsevier]

Multiwalled carbon nanotubes (MWNTs) were treated with a mixture of concentrated sulfuric and nitric acid to introduce carboxylic acid groups to the nanotubes. Conducting polymer film was prepared by electrochemical polymerization of neutral red (NR). By using a layer-by-layer method, homogeneous and stable MWNTs and poly (neutral red) (PNR) multilayer films were alternately assembled on glassy carbon (GC) electrodes. With the introduction of PNR, the MWNTs/PNR multilayer film system showed synergy between the MWNTs and PNR, with a significant improvement of redox activity due to the excellent electron-transfer ability of carbon nanotubes (CNTs) and PNR. The electropolymerization is advantageous, providing both prolonged long-term stability and improved catalytic activity of the resulting modified electrodes. The MWNTs/PNR multilayer film modified glassy carbon electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. As compared to MWNTs and PNR-modified GC electrodes, the magnitude of the amperometric response of the MWNTs/PNR composite-modified GC electrode is more than three-fold greater than that of the MWNTs modified GC electrode, and nine-fold greater than that of the PNR-modified GC electrode. With the immobilization of glucose oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to glucose has been constructed. In pH 6.98 phosphate buffer, nearly interference-free determination of glucose has been realized at -0.2 V vs. SCE with a linear range from 50 μM to 10mM and response time < 10s. The detection limit was 10 μM glucose (S/N = 3). [ABSTRACT FROM AUTHOR]

Abstract: Cobalt hexacyanoferrate nanoparticles (CoNP) can be easily prepared by mixing hexacyanoferrate and cobalt chloride solution at room temperature. The nanoparticles were solubilized in aqueous solution of a biopolymer chitosan (CHIT). With the introduction of carbon nanotubes (CNT), the CoNP–CNT–CHIT system formed shows synergy between CNT and CoNP with the significant improvement of redox activity of CoNP due to the excellent electron-transfer ability of CNT. The CoNP–CNT–CHIT film modified glassy carbon electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. In particular, with the introduction of CNT, it amplified the H2O2 sensitivity by ∼70 times compared to film of CoNP–CHIT. With the immobilization of glucose oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to glucose has been constructed. In pH 6.98 phosphate buffer, interference free determination of glucose has been realized at −0.2V versus saturated calomel electrode (SCE) with a linear range from 0.01 to 10mM and response time <10s. The detection limit was 5μM glucose (S/N=3). [Copyright &y& Elsevier]

Abstract: Platinum nanoparticle-doped sol–gel solution is prepared and used as a binder for multi-walled carbon nanotubes (CNT) for the fabrication of electrochemical sensors. Amine group containing sol–gel solution is selected to utilize the affinity of –NH2 groups toward metal nanoparticles for stabilization the nanoparticles in solution. The resulting CNT-silicate material brings new capabilities for electrochemical devices by using the synergistic action of the electrocatalytic activity of Pt nanoparticles and CNT. The combined electrocatalytic activity permits low-potential detection of hydrogen peroxide with remarkably improved sensitivity. With the incorporation of glucose oxidase within the Pt-CNT-silicate matrix, a Pt-CNT paste-based biosensor has been constructed that responds more sensitively to glucose than CNT-based biosensor. The influences of the composite of the sol–gel solution, the quantity of the solution and the Pt nanoparticles loading are examined. In pH 6.98 phosphate buffer, almost interference free determination of glucose is realized at 0.1V versus SCE with a linear range from 1 to 25mM, a response time <15s, and the sensitivity is 0.98μAmM−1 cm−2. The sensitivity of the Pt-CNT paste-based biosensor is almost four times larger than that of the CNT-based biosensor (0.27μAmM−1 cm−2 at 0.1V). The improved electrocatalytic activity and surface renewability made the Pt-CNT-silicate system a potential platform to immobilize different enzymes for other bioelectrochemical applications. [Copyright &y& Elsevier]

Abstract: Platinum nanoparticle-doped chitosan (CHIT) solution can be easily prepared by treating the CHIT solution with aqueous H2PtCl6 solution followed by chemical reduction of Pt(IV) with NaBH4. Multiwalled carbon nanotubes (MWCNT) are then dispersed in the nanoparticle-doped solution. The resulting Pt-CNT-CHIT material brings new capabilities for electrochemical devices by using the synergistic action of Pt nanaoparticles and CNT. Positively charged Pt-CNT-CHIT solution and negatively charged poly(sodium-p-styrenesulfonate) salt (PSS) have been employed to fabricate stable ultrathin multilayer films on gold electrode and quartz glass slides in a layer-by-layer fashion. Cyclic voltammetric and UV–vis adsorption spectroscopy confirms the consecutive growth of the multilayer films. The modified gold electrode allows low-potential detection of hydrogen peroxide with high sensitivity and fast response time. With the immobilization of cholesterol oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to cholesterol has been constructed. In pH 6.98 phosphate buffer, almost interference free determination of cholesterol has been realized at 0.1V vs. SCE with a linear range from 0.01 to 3mM and response time&#60;30s. With the immobilization of another cholesterol esterase enzyme layer, the biosensor was used to determine total cholesterol in serum samples with satisfactory results. [Copyright &y& Elsevier]

Abstract: Amperometric enzyme biosensors for the determination of acetylcholine (ACh) and choline (Ch) have been described. For the fabrication of the biosensors, N-acetylaniline (nAN) was first electropolymerized on a Pt electrode surface to be served as a permselective layer to reject interferences. Bovine serum albumin (BSA) and choline oxidase (CHOD) were co-immobilized in a zinc oxide (ZnO) sol–gel membrane on the above modified Pt electrode for a Ch sensor, or CHOD, acetylcholinesterase (AChE) and BSA immobilized together for an ACh/Ch sensor. The poly (N-acetylaniline) (pnAN) film was the first time used for an ACh/Ch sensor and found to have excellent anti-interference ability, and the BSA in the sol–gel can improve the stability and activity of the enzymes. Amperometric detection of ACh and Ch were realized at an applied potential of +0.6V versus SCE. The resulting sensors were characterized by fast response, expanded linear range and low interference from endogenous electroactive species. Temperature and pH dependence and stability of the sensor were investigated. The optimal ACh/Ch sensor gave a linear response range of 1.0×10-6 to 1.5×10-3M to ACh with a detection limit (S/N=3) of 6.0×10-7M and a linear response range up to 1.6×10-3M to Ch with a detection limit of 5.0×10-7M. The biosensor demonstrated a 95% response within less than 10s. [Copyright &y& Elsevier]

An amperometric enzyme biosensor for the determination of choline utilizing two enzymes, choline oxidase (CHOD) and horseradish peroxidase (HRP), is described. The biosensor consisted of CHOD cross-linked onto a HRP-immobilized carbon paste electrode. The biosensor was prepared by in situ electropolymerization of poly(thionine) within a carbon paste containing the enzyme HRP and thionine monomer and then CHOD was immobilized by using chitosan film through cross-linking with glutaraldehyde. The in situ electrogenerated poly(thionine) displays excellent electron transform efficiency between the enzyme HRP and the electrode surface, and the polymer enables improvement in enzyme immobilization within the paste. Several parameters such as the amount of thionine and enzyme, the applied potential, the pH, etc. have been studied. Amperometric detection of choline was realized at an applied potential of −0.2V vs saturated calomel electrode in 1/15M phosphate buffer solution (pH 7.4) with a linear response range between 5.0×10−6 and 6.0×10−4M choline and a response time of 15s. When applied to the analysis of phosphatidylcholine in serum samples, a 0.997 correlation was obtained between the biosensor results and those obtained by a hospital method. [Copyright &y& Elsevier]

An amperometric horseradish peroxidase (HRP) inhibition biosensor based on a thiolate self-assembled monolayer (SAM) has been developed for the determination of sulfides (HS-, H2S and small amount S2-). Cysteamine SAM was applied to the gold electrode surface and HRP was then immobilized on the electrode by cross-linking with glutaraldehyde. The measurement was performed in the presence of an electron mediator hydroquinone and 0.067 M phosphate buffer of pH 6.5 at an applied potential of -150 mV versus SCE. The determination of sulfides can be achieved in the range of 0.5–12.7 μM with a detection limit of 0.3 μM. The kinetic parameters Michaelis–Menten constant (Kmapp) and maximum current (Imax) with and without inhibitor have also been calculated and possible mechanism has been deduced according to the variation of Kmapp. [Copyright &y& Elsevier]

A rapid, simple method for fabricating glucose biosensors have been proposed for the efficient immobilization of enzymes and elimination of interferences at the same time. By using a single biopolymer chitosan on Pt electrode, first positively charged polyelectrolyte was constructed through glutaraldehyde as a cross-linking agent so that this kind of chitosan modified film can eliminate interference of possible electroactive compounds. Then another layer of chitosan was applied to immobilize enzyme glucose oxidase. The biosensor was operated at +0.600 V with a short response time (<8 s). The biosensor was free of typical interference, and cost-effective. The potential responses of the glucose sensor increase with the glucose concentration over the concentration range 0.05–15 mM, with high sensitivity (21 mA M-1 cm-2), and the detection limit is 10 μM. Furthermore, the biosensor exhibited long-term stability, and good reproducibility. The biosensors were applied to determination of glucose in beverage drinks. [Copyright &y& Elsevier]

A simple and sensitive immunosensor for the detection of cancer biomarker prostate specific antigen (PSA) has been developed. Around the percolation threshold of the graphene film, the conductivity of the graphene film varies significantly with the surface adsorption of molecules, which can be used for the detection of proteins based on antibody–antigen binding. [ABSTRACT FROM AUTHOR]

A polycytosine DNA-based immunosensor for electrochemical detection was developed and tested for detection of human epidermal growth factor receptor 2 (HER2), a breast cancer biomarker. We utilized gold nanoparticles (AuNPs) as supporting matrix to immobilize polycytosine DNA sequence (dC20) for electrochemical current generation and anti-HER2 antibodies. In the presence of target HER2, a sandwiched immunocomplex forms between a peptide specific to HER2 immobilized on the gold electrode and the anti-HER2 antibodies on the AuNPs. The HER2 captured by the sensor is detected because of the reaction of the dC20 phosphate backbone with molybdate, forming redox molybdophosphate precipitate that generates an electrochemical current on the surface of the electrode. The assay is sensitive: the calculated limit of detection of HER2 was as low as 0.5 pg/mL and the detection was linear to HER2 from 1 pg/mL to 1 ng/mL. The sensor's specificity is high, and there is no cross reactivity with several potential interferents, such as human IgG, human IgA, p53, carcinoembryonic antigen, and protein kinase. The sensor's performance with HER2 in clinical serum samples is similar to the performance of commercial ELISA assays. The configuration of polycytosine DNA as electrochemical current generating label and anti-HER2 antibodies on AuNPs is versatile and can be reconfigured to detect low levels of different analytes, or made more sensitive by amplifying the DNA to produce more phosphate to react with Na2MoO4. [ABSTRACT FROM AUTHOR]

Abstract: A new electrochemical immunosensor for the detection of protein biomarker platelet-derived growth factor BB (PDGF-BB) was developed based on graphene oxide (GO) initiated silver enhancement. The immunosensor was fabricated based on the traditional sandwich protocol using secondary anti-PDGF-BB antibody (Ab2) modified GO as label. Gold electrode was first modified with self-assembled monolayer (SAM) to block the electron transfer between the electrode and K3Fe(CN)6 solution. After the immobilization of primary anti-PDGF-BB antibody (Ab1) onto electrode via aminidation to the carboxylic group of SAM and the formation of the sandwich immuno-structure onto electrode surface, the electrode was immersed into silver enhancement solution for silver deposition. The deposited metal silver onto GO then mediated electron transfer across the SAM, producing redox current. The resulting immunosensor displays a wide range of linear response, low detection limit, good reproducibility and stability. The immunosensor was used to the detection of PDGF-BB contents in serum samples with satisfactory results. [Copyright &y& Elsevier]

Abstract: In this paper, for the first time, we introduced the seed-mediated method to the growth of cobalt hexacyanoferrate nanoparticles (CoNPs), using 3.5nm gold nanoparticles as seeds and multiwalled carbon nanotubes (MWCNTs) as growth scaffold which would both show synergistic action toward the reduction of H2O2. Via gold seeds, the one-step fabrication of CoNPs on the glassy carbon electrode is simple without any linking reagents, which will ingeniously exert the electrochemical properties of cobalt hexacyanoferrate. Combined with glucose oxidase, the sensing surface is applied as a biosensor for glucose. The growth of CoNPs is a chemical deposition process around the small Au nanoseed particles. The nanoseeds bridge the CoNPs and CNTs to form a smart nanocomposite. Spherical CoNPs have a relatively moderate dispersion on the three-dimensional network of CNTs with relatively even diameter ca. 100nm. Whereas, in the control experiments without gold seeds cobalt hexacyanoferrate can only form continuous films, of which the size is far from nanolevel and the catalytic ability is poor. The synthesis and fabrication/modification of CoNPs are simple and fast without prior preparation of CoNPs and lengthy process of cross-linking. The amount of the seeds and CNTs, growth time and concentration of growth solution were investigated. Scanning electron microscopy (SEM) and electrochemical method were used. [Copyright &y& Elsevier]

A surface treated nanoporous ZrO2/Chitosan composite matrix was developed to fabricate the glucose biosensor. This material combined the advantages of inorganic nanoparticles, ZrO2, and organic polymer, Chitosan. Glucose oxidase immobilized in the material maintained its activity well as the usage of glutaraldehyde was avoided. The activity of enzyme was 5.02 times greater than the cross-linked enzyme. The interaction between ZrO2/Chitosan and enzyme was characterized with FT-IR spectroscopy. The results of transmission electron microscopy of surface-treated ZrO2/Chitosan film showed that the matrix was porous and highly homogeneous. The parameters affecting the fabrication and experimental conditions of biosensors were optimized. The biosensor had a fast response of less than 10s. The linear range was 1.25 × 10-5 to 9.5 × 10-3M with a detection limit of 1.0 × 10-5M at 3σ and a sensitivity of 0.028μAmM-1. The biosensor retained about 75.2% of its original response after one-month storage in a phosphate buffer. [Copyright &y& Elsevier]

We have developed a new DNA self-assembly amplification technology that generates electric current for electrochemical biosensing. The new technology was used for detection of human epidermal growth factor receptor 2 (HER2). In our technology, an aptamer was utilized both as a ligand for recognition and as a signal generating reporter. The aptasensor is based on a sandwich format and a DNA primer on a HER2 aptamer initiates auxiliary DNA self-assembled on the electrode to form a long one-dimensional DNA. The resulting DNA is then reacted with molybdate to generate electrochemical current. The sensitivity of the aptasensor with DNA self- assembly was greater than that of the aptasensor without DNA self-assembly due to the extended length of the DNA strand. Aptasensor analysis of HER2 in serum of breast cancer patients and healthy individuals is highly correlated (R² = 0.9924) with ELISA measurements, with a p value of 1.37 x 10-7. The analysis of HER2 in serum (confirmed by ELISA) suggests that HER2 levels in breast cancer patients are much higher than healthy individuals. For HER2 positive patients, the levels are higher than those of HER2 negative patients. After surgery, there is a drop of HER2 levels in serum, suggesting potential clinical applications of the new self-assembled DNA electric current generating biosensor. Unlike proteins, DNA is easily amplifiable. The DNA signal amplification method presented here enables effective current generation, which can find wide range of biomedical applications for protein detection. [ABSTRACT FROM AUTHOR]

Protein kinase (PKA) and alkaline phosphatase (ALP) are clinically relevant enzymes for a number of diseases. In this work, we developed a new simple electrochemical biosensor for the detection of the activity and inhibition of both PKA and ALP. One common feature of the PKA and ALP catalyzing process is that PKA can hydrolysis adenosine-5′-triphosphate (ATP) and ALP can hydrolysis pyrophosphate, both reactions produce phosphate ions, and the amount of phosphate ion produced is proportional to enzyme activity. Our assay is based on the principle that phosphate ions react with molybdate to form redox molybdophosphate precipitates on the electrode surface, thus generating electrochemical current. The detection limit for PKA and ALP were much lower than existing assays. The biosensor has good specificity and was used to measure drug-stimulated PKA from lysates of HeLa cells. We also evaluated the use of the biosensor as a screening tool for enzyme inhibitors. To the best of our knowledge, this is the first report of a biosensor capable of detecting the activity of both PKA and ALP. This tool has the potential to simplify PKA and ALP clinical measurement, thereby improving diagnostics of relevant diseases. It also may serve as the basis for a simple screening method for new enzyme inhibitors for disease treatment. [ABSTRACT FROM AUTHOR]

Abstract: Sensitive electrochemical immunosensor for the detection of interleukin-17 (IL-17) was prepared using cadmium (Cd2+) ion incorporated polystyrene sphere (PS, PS–Cd2+) as label. With the linking of the detection anti-IL-17 antibody (Ab2) onto PS (PS–Cd2+–Ab2), the modified PS can be captured onto the electrode surface through immuno-reaction. Tetrahydrofuran (THF) was then dropped onto the electrode surface to dissolve the PS and release the contained Cd2+ ions onto electrode surface for the following stripping voltammetric detection. Compared to the electrochemical label based on quantum dots (QD), this method for the detection of Cd2+ ion is much simpler and straightforward. With the immobilization of primary anti-IL-17 antibody (Ab1) onto graphene surface, the resulting immunosensor displays high sensitivity, which can be ascribed to the significant number of Cd2+ ions incorporated into PS and a large number of Ab2 linked onto PS surface. The response current was linear to the logarithm of IL-17 concentration in the range from 0.1pg to 1ng/mL with a detection limit of 50fg/mL. The immunosensor results were validated through the detection of IL-17 in serum samples with satisfactory results. [Copyright &y& Elsevier]

Abstract: A novel kind of hydrogel was prepared from ferrocene (Fc) functionalized amino acid phenylalanine (Phe) and applied for the fabrication of electrochemical immunosensor to detect tumor necrosis factor α (TNF-α). The prepared hydrogel displays high redox activity due to the incorporation of a significant number of Fc moieties into the hydrogel. When the hydrogel was reacted with ascorbic acid (AA), the redox activity of the hydrogel was decreased as the Fc moieties in the hydrogel were reduced by AA. Based on this phenomenon, the immunosensor was constructed utilizing the traditional sandwich format using the hydrogel modified electrode as sensing platform and alkaline phosphatase (ALP) modified polystyrene sphere (PS) as label. First, primary anti-TNF-α antibody was immobilized onto the electrode surface via gold nanoparticles (AuNPs), then TNF-α and ALP were sequentially captured onto electrode. The ALP captured onto the electrode will catalyzes the hydrolysis of ascorbic acid 2-phosphate (AA-p) to form AA. The latter, in return, will cause the decrease of the redox current of the electrode. The decrease of the redox current is proportional to the concentration of TNF-α detected in the range from 1pg/mL to 10ng/mL. The immunosensor testing results were validated through the detection of clinical serum sample with satisfactory results. [Copyright &y& Elsevier]

Abstract: Sensitive electrochemical immunosensor for the detection of protein biomarker tumor necrosis factor α (TNF-α) was reported that uses ferrocene carboxylic acid (Fc) functionalized self-assembled peptide nanowire (Fc-PNW) as sensor platform and glucose oxidase (GOx) modified gold nanorod (GNR) as label. Greatly enhanced sensitivity is achieved based on a dual signal amplification strategy: first, the synthesized Fc-PNW used as the sensor platform increased the loading of primary anti-TNF-α antibody (Ab1) onto electrode surface due to its large surface area. At the same time, the Fc moiety on the nanowire is used as a mediator for GOx to catalyze the glucose reaction. Second, multiple GOx and secondary anti-TNF-α antibody (Ab2) molecules are bounded onto each GNR to increase the sensitivity of the immunosensor. After the preparation of the immunosensor based on the traditional sandwich protocol, the response of the immunosensor towards glucose was used as a signal to differentiate various concentrations of TNF-α. The resulting immunosensor has high sensitivity, wide linear range (0.005–10ng/mL) and good selectivity. This immunosensor preparation strategy is a promising platform for clinical screening of protein biomarkers. [Copyright &y& Elsevier]

Abstract: A sandwich electrochemical immunosensor for the sensitive determination of alpha fetoprotein (AFP) has been fabricated. Prussian blue modified hydroxyapatite (PB@HAP) was firstly prepared and used as electrochemical label due to the wonderful conductivity and good biocompatibility of HAP. The results proved that the immunosensor fabricated using the label based on PB@HAP loaded with horse radish peroxidase (HRP) and secondary anti-AFP antibody (Ab2) (PB@HAP-HRP-Ab2) had high sensitivity, and the sensitivity of the label PB@HAP-HRP-Ab2 was much higher than labels of PB@HAP-Ab2, PB-HRP-Ab2 and HAP-HRP-Ab2. The mixture of graphene sheet (GS) and thionine (TH) was not only used to immobilize anti-AFP antibody (Ab1) but also took part in the signal amplification. The amperometric signal increased linearly with AFP concentration in the range of 0.02–8ng/mL with a low detection limit of 9pg/mL. The immunosensor had the advantages of high sensitivity, good selectivity and good stability, and was applied to the analysis of AFP in serum sample with satisfactory results. Due to the low-cost and easy synthesis of PB@HAP, the screen-printed electrodes could be used instead of the bare glass carbon electrode in order to achieve mass production. In addition, it had potential application in the detection of other tumor markers. [Copyright &y& Elsevier]

Abstract: A novel method to construct amperometric immunosensor for human serum chorionic gonadotrophin (hCG) has been described. In this study, horseradish peroxidase (HRP), Pt nanoparticles and secondary antibody (Ab2) modified MSN (Pt@MSN/HRP/Ab2) was synthesized and the multifunctional MSN was used as label for the preparation of immunosensor. With the hCG primary antibody immobilized onto thionine/graphene modified glassy carbon electrode (GCE) via crosslinking with glutaraldehyde, the electrochemical immunosensor was able to realize a reliable determination of hCG in the range of 0.01–12ngmL−1 with a detection limit of 7.50pgmL−1. This immunoassay system has many desirable merits including high sensitivity, accuracy, and little instrumentation requirement. Significantly, the new method may be quite promising, with potentially broad applications for clinical immunoassays. [Copyright &y& Elsevier]

Abstract: In this study, amino group modified mesoporous silica nanoparticles (MSN) were prepared and used to immobilize both platinum nanoparticles (PtNP) and glucose oxidase (GOx). The prepared MSN–PtNP demonstrated high stability and reactivity for catalyzing H2O2 electro-reduction, mainly due to the large amount of PtNP immobilized, the high surface area of these catalysts and the unique nanostructures formed through the synthetic route. Working at −0.2V, the linear range in response to H2O2 by the prepared MSN–PtNP can be 5×10−7 to 6×10−2 molL−1. After immobilizing GOx onto MSN–PtNP, the resulting MSN–PtNP–GOx was capable of interference-free determination of glucose with the linear range as wide as 1×10−6 to 2.6×10−2 molL−1. Furthermore, the fabricated glucose biosensor can offer significant advantages compared with its conventional counterparts, typically like the high sensitivity, good reproducibility and stability, and rapid response ability as well. The fabricated glucose biosensor demonstrated its potential in clinical applications, so as to enable the determination of glucose in real serum samples. [Copyright &y& Elsevier]

Abstract: A novel electrochemical immunosensor for sensitive detection of cancer biomarker prostate specific antigen (PSA) based on nitrodopamine (NDA) functionalized iron oxide nanoparticles (NDA–Fe3O4) is described. NDA–Fe3O4 was used both for the immobilization of primary anti-PSA antibody (Ab1) and as secondary anti-PSA antibody (Ab2) label. For the preparation of the label, mediator thionine (TH) was first conjugated onto NDA–Fe3O4 based on the amino groups of NDA, and then the amino group of TH was used to immobilize horseradish peroxidase (HRP) and Ab2. Due to the high amount of NDA anchored onto Fe3O4 surface, the loading of antibodies as well as mediator and enzyme onto NDA–Fe3O4 was substantially increased, which increased the sensitivity of the immunosensor. The resulting immunosensor displayed a wide range of linear response (0.005–50ng/mL), low detection limit (4pg/mL), good reproducibility and stability. The immunosensor was used to detect the PSA contents in serum samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we developed a novel kind of label based on dumbbell-like Au-Fe3O4 nanoparticles (NPs) for the preparation of electrochemical immunosensor for the detection of cancer biomarker prostate specific antigen (PSA). The signal amplification strategy, using the synergetic effect present in Au-Fe3O4 to increase the reduction ability of the NPs toward H2O2, improves the sensitivity and detection limit of the immunosensor. With primary anti-PSA antibody (Ab1) immobilized onto graphene surface and secondary anti-PSA antibody (Ab2) adsorbed onto the Au of the Au-Fe3O4 NPs, the immunosensor prepared through a sandwich structure displays a wide linear range (0.01–10ng/mL), low detection limit (5pg/mL), good reproducibility and stability. These labels for immunosensors may provide many potential applications for the detection of different biomolecules. [ABSTRACT FROM AUTHOR]

In this work, a sensitive and reliable photoelectrochemical (PEC) biosensor was proposed based on hexagonal carbon nitride tubes (HCNT) as photoactive material for detection of circulating tumor cells (CTCs). Magnetic Fe 3 O 4 nanospheres (MNs) and Cu 2 O nanoparticles (Cu 2 O NPs) were utilized for highly efficient magnetic capture of CTCs and for signal amplification, respectively. First, anti-epithelial cell adhesion molecule (EpCAM) antibody was linked onto MNs for capture and enrichment of CTCs. With the captured MCF-7 coated onto the electrode, the photocurrent intensity of HCNT was decreased due to the steric hindrance derived from MCF-7. Then, when the Cu 2 O-aptamer probe was bound onto the CTC surface, the photocurrent intensity was further decreased because Cu 2 O NPs competed with HCNT for absorption of exciting light and the aptamer molecules increased the steric hindrance, which leads to significantly decreased photocurrent response, thus realizing dual signal amplification. Using the breast cancer cell MCF-7 as a model, the proposed PEC biosensor displays good performances with a linear range from 3 to 3000 cell mL−1 and limit of detection down to 1 cell mL−1. The HCNT-based PEC biosensor shows good performance for detection of CTCs, which may have potential applications in cancer diagnostics and therapeutics. • Dual signal amplification strategy was reported for detecting circulating tumor cells. • Magnetic nanospheres were used for efficient capture of cells. • Cu 2 O nanoparticles were tested for signal amplification. • The detection of cells was based on the suppression of current intensity. • The biosensor was applied for detection of tumor cells in blood sample. [ABSTRACT FROM AUTHOR]