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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]

Graphene material has been widely used for optical sensors owing to its excellent properties, including high-energy transfer efficiency, large surface area, and great biocompatibility. Different analytes such as nucleic acids, proteins, and small molecules can be detected by graphene-material-based optical sensors. This review provides a comprehensive discussion of graphene-material-based optical sensors focusing on detection mechanisms and biosensor designs. Challenges and future perspectives for graphene-material-based optical sensors are also presented. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a novel electrochemical DNA sensor for the simple, sensitive and specific detection of nucleic acids based on proximity-dependent DNA ligation assays with the DNAzyme amplification of hairpin substrate signal. A long DNA strand contains the catalytic motif of Mg2+-dependent 10-23 DNAzyme, acting as the recognition probe. When the target DNA was introduced into the system, part of it was complementary to 5′-end of the recognition probe, resulting in the ligation of a stable duplex, the unbinded part of the target DNA was acted as one binding arm for the DNAzyme. This duplex containing a complete 10-23 DNAzyme structure could cleave the purine–pyrimidine cleavage site of the hairpin substrate, which resulted in the fragmentation of the hairpin structure and the release of two single-stranded nucleic acids, one of which was biotinylated and acted as the signal probe. An immobilized thiolated capture probe could bind with the signal probe, using biotin as a tracer in the signal probe, and streptavidin–alkaline phosphatase (SA–ALP) as reporter molecule. The activity of the immobilized enzyme was voltammetrically determined by measuring the amount of 1-naphthol generated after 5min of enzymatic dephosphorylation of 1-naphthyl phosphate. The results revealed that the sensor showed a sensitive response to complementary target sequences of H. pylori in a concentration range from 100fM to 1nM, with a detection limit of 50fM. In addition, the sensing system could discriminate the complementary sequence from mismatched sequences, with high sensitivity and reusability. [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]

Enzyme-free, signal-amplified nucleic acid circuits utilize programmed assembly reactions between nucleic acid substrates to transduce a chemical input into an amplified detection signal. These circuits have shown great potential for developing biosensors for high-sensitivity and high-selectivity detection of varying targets including nucleic acids, small molecules and proteins in vitro and for high-contrast in situ visualization and imaging of these targets in tissues and living cells. We review the background of the enzyme-free, signal-amplified nucleic acid circuits, including their mechanism, significance, types and development. We also review current applications of these circuits for biosensors and bioimaging. [ABSTRACT FROM AUTHOR]

A label-free fluorescence aptamer-based sensor method for cocaine detection has been constructed based on polymerase aided isothermal circular strand-displacement amplification (ICSDA) and graphene oxide (GO) absorption. In this assay, a hairpin probe (HP), which consists of the aptamer sequence of cocaine, is partially complementary to the primer. When cocaine was bound with the HP, the primer could anneal with the single-stranded sequence of the opened HP and then trigger polymerase elongation, generating a double-stranded DNA (dsDNA) and displacing the cocaine. In the absence of cocaine, the HP remained intact and ICSDA would not occur. Through combining the unique properties of SYBR Green I (SG) and the preferential binding of GO to single-stranded DNA over dsDNA, a significant fluorescence enhancement was achieved. Whereas, the SG-stained HP without polymerase elongation was absorbed and quenched by GO. The proposed method is simple, convenient, and has high sensitivity and selectivity. This method displayed a good linear correlation within the cocaine concentration range from 0.2 μM to 100 μM, and the detection limit was down to 190 nM. In addition, this aptamer-based sensor method was also successfully applied for cocaine quantification in human urine samples. [ABSTRACT FROM AUTHOR]

A label-free fluorescent DNA biosensor has been presented based on isothermal circular strand-displacement polymerization reaction (ICSDPR) combined with graphene oxide (GO) binding. The proposed method is simple and cost-effective with a low detection limit of 4 pM, which compares favorably with other GO-based homogenous DNA detection methods. [ABSTRACT FROM AUTHOR]

Abstract: The combination of aptamers with novel nanomaterials, including nanomaterial-based aptamer bioconjugates has attracted considerable interest and has led to a wide variety of applications. In this review, we discuss how a variety of nanomaterials, including gold, silica and magnetic nanoparticles, as well as carbon nanotubes, hydrogels, liposomes and micelles, have been used to functionalize aptamers for a variety of applications. These aptamer functionalized materials have led to advances in amplified biosensing, cancer cell-specific recognition, high-efficiency separation, and targeted drug delivery. [Copyright &y& Elsevier]

Abstract: In this work, an aptazyme-based electrochemical biosensor for the detection of adenosine is reported. Aptazyme activity was modulated by appending an “inhibitor” oligonucleotide strand containing a 32-base adenosine aptamer to the 8-17 DNAzyme. In the absence of adenosine, the DNAzyme could not form appropriate catalytic structure due to the binding with the inhibitor strand. Upon adenosine binding to the aptamer, the inhibitor strand was dissociated from the DNAzyme sequence. This allowed the DNAzyme to open and bind with the hairpin substrate, and DNAzyme activity was thereby induced, cleaving the substrate at its ribonucleotide site in the presence of Pb2+. Cleavage of the substrate yields two single-stranded products, one of which was ferrocene-tagged and acted as the signal probe. The thiolated probe modified on the gold electrode could capture the signal probe. As a result, the ferrocene (Fc) moiety was brought in close proximity to the electrode surface and the Faradaic current was observed. This electrochemical biosensor was proved to have a wide dynamic range from 5nM to 2000nM with a detection limit of 5nM. The fabricated sensor is shown to exhibit high sensitivity and desirable selectivity, which might be promising for the rational construction of aptazyme-based biosensors and the determination of adenosine in clinical examination. [Copyright &y& Elsevier]

Abstract: A simple, rapid and highly sensitive piezoelectric immunosensor has been proposed and applied to detect aflatoxin B1 (AFB1). It is unlikely that direct binding of small molecules such like AFB1 to the piezoelectric sensor surface could result in a satisfactory detection limit and sensitivity. Thus, indirect competitive immunoassay technique had been used for the detection of the target and gold nanoparticles (GNP) been employed as a ‘weight label’ to the secondary antibody for amplifying the response. This method is proven in its ability to detect AFB1 down to a level of 0.01ngmL−1 in artificially contaminated milk, which is comparable to or even exceeding the sensitivity of microtitre plate ELISA. Furthermore, the frequency responses of the immunoassay are linearly correlated to the logarithm of AFB1 concentration in the range of 0.1–100ngmL−1. The sensor could be regenerated under very mild conditions simply by immersing the sensor into glycine buffer solution to desorb the combined antibody. It is found that the as-renewed sensor could be reused at least 9 runs without obvious loss of sensing sensitivity. [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]