Graphene as a signal amplifier for preparation of ultrasensitive electrochemical biosensors

Early diagnostics of diseases performed with minimal money and time consumption has become achievable due to recent advances in development of biosensors. These devices use biorecognition elements for selective interaction with an analyte and signal readout is obtained via different types of transducers. Operational characteristics of biosensors have been reported to improve substantially, when a diverse range of nanomaterials was employed. This review presents construction of electrochemical biosensors based on graphene, atomically thin 2D carbon crystals, which is currently intensively studied nanomaterial. The most attractive directions of graphene applications in biosensor preparation are discussed here including novel detection and amplification schemes exploiting graphene's unique electrochemical, physical and chemical properties. The future of graphene-based biosensors is most likely bright, but there is still a lot of work to do to fulfill high expectations.

Gold nanorods-paper electrode based enzyme-free electrochemical immunoassay for prostate specific antigen using porous zinc oxide spheres–silver nanoparticles nanocomposites as labels

Gold nanorods-modified paper electrode and porous zinc oxide spheres–silver nanoparticles nanocomposites were used to construct an enzyme-free immunosensor.

Multiplexing determination of lung cancer biomarkers using electrochemical and surface-enhanced Raman spectroscopic techniques

A reliable immunosensor for simultaneous detection of carcinoembryonic antigen and cytokeratin-19 by complementary advantages of the electrochemical and SERS technologies.

Multiplexed detection of two proteins by a reaction kinetics-resolved chemiluminescence immunoassay strategy

A multiplexed immunoassay method was proposed for the sequential detection of two proteins based on a novel chemiluminescence reaction kinetics-resolved strategy.

A disposable paper-based electrochemiluminescence device for ultrasensitive monitoring of CEA based on Ru(bpy)32+@Au nanocages

Ultrasensitive detection of CEA based on Ag nanospheres modified paper working electrode platform and Ru(bpy)₃²⁺@Au nanocages signal amplification.

Novel gold-decorated polyaniline derivatives as redox-active species for simultaneous detection of three biomarkers of lung cancer

Novel redox-active species including gold-poly(o-aminophenol) and gold-poly(p-phenylenediamine) were synthesized and applied for the electrochemical immunoassay of three tumor biomarkers.

Multiplexed electrochemical detection of trypsin and chymotrypsin based on distinguishable signal nanoprobes

In this work, we developed a novel multisignal output for simultaneous detection of multiple proteases by using nanoprobes labeled with distinguishable electrochemical probes. First, biotinylated peptide1 (S1) and biotinylated peptide2 (S2) were associated with biotinylated DNA1 and DNA2 via biotin-streptavidin interaction, forming DNA1-S1 and DNA2-S2, respectively. Two distinguishable signal nanoprobes (DNA1'-Au NPs-Thi and DNA2'-Au NPs-Fc) were prepared by initial assembling DNA1' and DNA2' on the Au NPs surface, respectively, and then carrying corresponding thionine (Thi) and 6-(Ferrocenyl)hexanethiol (Fc). Then, the peptide substrates (DNA1-S1 and DNA2-S2) were immobilized on gold electrode surface through Au-S bonds, and the DNA1'-Au NPs-Thi and DNA2'-Au NPs-Fc were assembled to the peptide-DNA-modified electrode surface via DNA hybridization. The targets of trypsin and chymotrypsin can specifically recognize and cleave peptides with different sequences, releasing DNA1'-Au NPs-Thi and DNA2'-Au NPs-Fc from the electrode surface into solution, thus decreasing the current of Thi and Fc. The decrease in the electrochemical currents of the two signal nanoprobes enables us to simultaneously and quantitatively determine the targets trypsin and chymotrypsin. More importantly, this strategy can be extended easily by designing various proteases-specific peptide substrates and utilizing corresponding electrochemical detectable elements for simultaneous multiplex protease assay in various biosystems.

Growth of gold-manganese oxide nanostructures on a 3D origami device for glucose-oxidase label based electrochemical immunosensor

Flexible biosensors are of considerable current interest for the development of portable point-of-care medical products, minimally invasive implantable devices, and compact diagnostic platforms. Here, we reported an electrochemical paper based analytical device fabricated (EPADs) by sequentially growing gold nanoparticles (AuNPs) and manganese oxide (MnO2) nanowires networks on a freestanding three dimensional (3D) origami device. This fabricated through the growth of an AuNPs layer on the surfaces of cellulose fibers in the screen-printed paper working electrode (PWE), and thus developed a gold paper working electrode (Au-PWE). Subsequently, MnO2 nanowires were successfully electrodeposited on Au-PWE to form a 3D network with large surface areas. Based on this novel EPADs and the principle of origami, we presented herein a simple immunosensing scheme using glucose oxidase (GOx) as an enzyme label, 3,3',5,5'-tetramethylbenzidine (TMB) as a redox terminator, and glucose as an enzyme substrate. The electrochemical enzymatic redox cycling was applied to the detection of prostate protein antigen (PSA), a biomarker of prostatic cancer. The proposed method successfully fulfilled the highly sensitive detection of PSA with a linear range of 0.005 ng mL(-1)-100 ng mL(-1) with a detection limit of 0.0012 ng mL(-1). This EPADs exhibited high sensitivity, specificity and excellent performance in real human serum assay, and could be applied in point-of-care testing of other tumor markers for remote regions and developing countries.

A novel label-free amperometric immunosensor for carcinoembryonic antigen based on Ag nanoparticle decorated infinite coordination polymer fibres

In this article, for the first time, a novel, high-yield and template-free method for the synthesis of Ag nanoparticle decorated thionine/infinite coordination polymer (AgNP/THI/ICP) fibres is proposed. The thionine can be adsorbed to the AgNP/THI/ICP fibres by π-conjugation and act as the redox probe. The AgNP/THI/ICP fibres not only favor the immobilization of antibody but also facilitate the electron transfer. It is found that the AgNP/THI/ICP fibres can be designed to act as a sensitive label-free electrochemical immunosensor for carcinoembryonic antigen (CEA) determination. Under the optimized conditions, the linear range of the proposed immunosensor is estimated to be from 50 fg/mL to 100 ng/mL and the detection limit is estimated to be 0.5 fg/mL at a signal-to-noise ratio of 3, respectively. The prepared immunosensor for detection of CEA shows high sensitivity, reproducibility and stability. Our study demonstrates that the proposed immunosensor has also been used to determine CEA successfully in diluted blood samples.

A paper disk equipped with graphene/polyaniline/Au nanoparticles/glucose oxidase biocomposite modified screen-printed electrode: toward whole blood glucose determination

In this work, a convenient, fast, low cost, small sample volume and in situ detection of glucose in human whole blood has been developed by using a disposable screen-printed carbon electrode (SPCE) coupled with a paper disk. To perform the assay, the SPCE was modified with graphene/polyaniline/Au nanoparticles/glucose oxidase (Gr/PANI/AuNPs/GOD) biocomposite and then covered by a paper disk impregnated with the sample. After introducing PBS on the paper disk, the electrochemical measurement was carried out. The assay was based on measuring the current decrease of flavin adenine dinucleotide (FAD) in GOD provoked by the enzyme-substrate reaction using differential pulse voltammetry (DPV). The analytical performance was comparable to conventional methods, and covered the full range of clinically relevant concentrations of glucose in whole blood. This new paper-based electrochemical glucose sensor shows promise in applying point-of-care (POC) device in whole blood tests, and particularly being appropriate for use in the developing world and in resource-limited settings.

Ultrasensitive multiplexed immunosensors for the simultaneous determination of endocrine disrupting compounds using Pt@SBA-15 as a non-enzymatic label

The simultaneous determination of different analytes based on multiplexed immunosensors is attractive and promising in bioassays and environmental analysis. In this paper, a novel ultrasensitive multiplexed immunoassay method was developed for the determination of endocrine disrupting compounds (EDCs) based on disposable screen-printed carbon electrodes. Different capture antibodies were separately immobilized on the carbon electrodes to form an immunosensor array. Platinum nanoparticle-functionalized mesoporous silica nanoparticles (Pt@SBA-15) was used as catalytic labels of secondary antibodies. Due to the catalytic activities of the platinum nanoparticles and the large surface area of SBA-15, a strong electrical response towards the analytical antigens was achieved. The multiplexed immunoassay array enables the simultaneous determination of different analytes. Using diethylstilbestrol and estradiol as model analytes, this multiplexed immunoassay method showed wide linear ranges with detection limits down to 0.28 and 1.2 pg mL^-1 for diethylstilbestrol and estradiol, respectively. The proposed sensing strategy enriches electrochemical immunoassays and has a promising application in bioassays and environmental analysis.