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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]

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: 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]

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: 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]

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 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 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]