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A novel electrochemical sensor was developed for sensitive and selective detection of mercury(II), based on thymine--[Hg.sup.2+]--thymine (T--[Hg.sup.2+]--T) coordination chemistry. This strategy exploited the cooperativity of proximate poly-T oligonucleotides in coordination with [Hg.sup.2+]. Ferrocene (Fc)-tagged poly-T oligonucleotides were immobilized on the electrode surface via self-assembly of the terminal thiol moiety. In the presence of [Hg.sup.2+], a pair of poly-T oligonucleotides could cooperatively coordinate with [Hg.sup.2+], which triggered a conformational reorganization of the poly-T oligonucleotides from flexible single strands to relatively rigid duplexlike complexes, thus drawing the Fc tags away from the electrode with a substantially decreased redox current. The response characteristics of the sensor were thoroughly investigated using capillary electrophoresis and electrochemical measurements. The results revealed that the sensor showed a sensitive response to [Hg.sup.2+] in a concentration range from 1.0 nM to 2.0 [micro]M, with a detection limit of 0.5 nM. Also, this strategy afforded exquisite selectivity for [Hg.sup.2+] against a reservoir of other environmentally related metal ions, compared to existing anodic stripping voltammetry (ASV) techniques. In addition, this sensor could be implemented using minimal reagents and working steps with excellent reusability through mild regeneration procedure. It was expected that this cost-effective electrochemical sensor might hold considerable potential in on-site applications of [Hg.sup.2+] detection.

Aptamer-based rolling circle amplification (aptamer-RCA) was developed as a novel versatile electrochemical platform for ultrasensitive detection of protein. This method utilized antibodies immobilized on the electrode surface to capture the protein target, and the surface-captured protein was then sandwiched by an aptamer-primer complex. The aptamer-primer sequence mediated an in situ RCA reaction that generated hundreds of copies of a circular DNA template. Detection of the amplified copies via enzymatic silver deposition then allowed enormous sensitivity enhancement in the assay of target protein. This novel aptamer-primer design circumvented time-consuming preparation of the antibody-DNA conjugate for the common immuno-RCA assay. Moreover, the detection strategy based on enzymatic silver deposition enabled a highly efficient readout of the RCA product as compared to a redox-labeled probe based procedure that might exhibit low detection efficiency due to RCA product distance from the electrode. With the platelet-derived growth factor B-chain (PDGF-BB) as a model target, it was demonstrated that the presented method was highly sensitive and specific with a wide detection range of 4 orders of magnitude and a detection limit as low as 10 fM. Because of the wide availability of aptamers for numerous proteins, this platform holds great promise in ultrasensitive immunoassay.

Monitoring aspects of human performance during various activities has recently become a highly investigated research area. Many new commercial products are available now to monitor human physical activity or responses while performing activities ranging from playing sports, to driving, and even sleeping. However, monitoring cognitive performance biomarkers, such as neuropeptides, is still an emerging field due to the complicated sample collection and processing, as well as the need for a clinical lab to perform analysis. Enzyme-linked immunosorbent assays (ELISAs) provide specific detection of biomolecules with high sensitivity (picomolar concentrations). Even with the advantage of high sensitivity, most ELISAs need to be performed in a laboratory setting and require around 6 h to complete. Transitioning this assay to a platform where it reduces cost, shortens assay time, and is able to be performed outside a lab is invaluable. Recently developed paper diagnostics provide an inexpensive platform on which to perform ELISAs; however, the major limiting factor for moving out of the laboratory environment is the measurement and analysis instrumentation. Using something as simple as a digital camera or camera-enabled Windows- or Android-based tablets, we are able to image paper-based ELISAs (P-ELISAs), perform image analysis, and produce response curves with high correlation to target biomolecule concentration in the 10 pM range. Neuropeptide Y detection was performed. Additionally, silver enhancement of Au NPs conjugated with IgG antibodies showed a concentration-dependent response to IgG, thus eliminating the need for an enzyme–substrate system. Automated image analysis and quantification of antigen concentrations are able to be performed on Windows- and Android-based mobile platforms. [ABSTRACT FROM AUTHOR]

β-Agonists fed to animals for human consumption pose a serious threat to human health. Fast, broad-spectrum detection methods are needed for on-site screening of various types of β-agonists from animal feeds, meats, and animal body fluids. We developed a colorimetric assay that uses gold nanoparticle (AuNP) plasmon absorption to realize quick detection of β-agonists from liquid samples. β-Agonists showed the capability of directly reducing HAuCl4 into atomic gold, which involved oxidation of the amine or phenol group on the benzene ring of the β-agonists. The resulting atomic gold formed AuNPs spontaneously, which had strong plasmon absorption at 528 nm. The linear relationship between the concentrations of β-agonists and the AuNPs plasmon absorbance granted quantitative determination of β-agonists in solution. The AuNPs colorimetric assay showed different sensitivities toward β-agonists with different substituent groups on the aromatic ring. β-Agonists with phenol groups had a lower limit of quantitation (LOQ) than those with amine groups. High-resolution transmission electron microscopy (TEM) images revealed the sizes of the AuNPs were in the range 15-25 nm, while X-ray energy-dispersive spectroscopic data suggested the smaller particles observed in TEM with lower contrast may be salt particles from the buffer solution. The developed colorimetric assay can potentially be used for the detection of β-agonists and their analogues from serum, urine, and other liquid samples in the presence of interference from common antibiotics and glucose. [ABSTRACT FROM AUTHOR]

An electrochemical DNAzyme sensor for sensitive and selective detection of lead ion (Pb2+) has been developed, taking advantage of catalytic reactions of a DNAzyme upon its binding to Pb2+ and the use of DNA-Au bio-bar codes to achieve signal enhancement. A specific DNAzyme for Pb2+ is immobilized onto an Au electrode surface via a thiol-Au interaction. The DNAzyme hybridizes to a specially designed complementary substrate strand that has an overhang, which in turn hybridizes to the DNA-Au biobar code (short oligonucleotides attached to 13 nm gold nanoparticles). A redox mediator, Ru(NH3)63+, which can bind to the anionic phosphate of DNA through electrostatic interactions, serves as the electrochemical signal transducer. Upon binding of Pb2+ to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand along with the DNA bio-bar code and the bound Ru(NH3)63+ from the Au electrode surface. The release of Ru(NH3)63+ results in lower electrochemical signal of Ru(NH3)63+ confined on the electrode surface. Differential pulse voltammetry (DPV) signals of Ru(NH3)63+ provides quantitative measures of the concentrations of Pb2+, with a linear calibration ranging from 5 nM to 0.1 μM. Because each nanoparticle carries a large number of DNA strands that bind to the signal transducer molecule Ru(NH3)63+, the use of DNA-Au bio-bar codes enhances the detection sensitivity by five times, enabling the detection of Pb2+ at a very low level (1 nM). The DPV signal response of the DNAzyme sensor is negligible for other divalent metal ions, indicating that the sensor is highly selective for Pb2+. Although this DNAzyme sensor is demonstrated for the detection of Pb2+, it has the potential to serve as a general platform for design sensors for other small molecules and heavy metal ions. [ABSTRACT FROM AUTHOR]

An ultrasensitive label-free bioelectrochemical method for rapid determination of thrombin has been developed by directly detecting the redox activity of adenine (A) nucleo-bases of anti-thrombin aptamer using a pyrolytic graphite electrode. The bioelectrochemical protocol involves a sandwich format. Thrombin, captured by immobilzed antithrombin antibody on microtiter plates, is detected by anti-thrombin aptamer-Au nanoparticle bio bar codes. A systematic optimization of the parameters has been earned out via ELAA (enzyme linked aptamer assay) performance. The adenine nucleobases were released by acid or nuclease from Au nanoparticles bound on microtiter plates. Differential pulse voltammetry was employed to investigate the electrochemical behaviors of the purine nucleobases. Well-defined adenine signal was observed at about 0.85 V in pH 5.9 acetate buffer. Because the nanoparticle carries a large number of aptamers per thrombin binding event, there is substantial amplification and thrombin can be detected at a very low level of detection (0.1 ng/mL). This method has been used to detect thrombin in complex matrix such as fetal calf serum with minimum background interference. [ABSTRACT FROM AUTHOR]

Aptamers are nucleic acids that have high affinity and selectivity for their target molecules. A target may induce the structure switching from a DNA/DNA duplex to a DNA/target complex. In the present study, a reusable electrochemical sensing platform based on structure-switching signaling aptamers for highly sensitive detection of small molecules is developed using adenosine as a model analyte. A gold electrode is first modified with polytyramine and gold nanoparticles. Then, thiolated capture probe is assembled onto the modified electrode surface via sulfur-gold affinity. Ferrocene (Fc)-labeled aptamer probe, which is designed to hybridize with capture DNA sequence and specifically recognize adenosine, is immobilized on the electrode surface by hybridization reaction. The introduction of adenosine triggers structure switching of the aptamer. As a result, Fc-labeled aptamer probe is forced to dissociate from the sensing interface, resulting in a decrease in redox current. The decrement of peak current is proportional to the amount of adenosine. The present sensing system could provide both a wide linear dynamic range and a low detection limit. In addition, high selectivity, good reproducibility, stability, and reusability are achieved. The recovery test demonstrates the feasibility of the designed sensing system for an adenosine assay. [ABSTRACT FROM AUTHOR]

Submicro- and nanometer-sized glass double-barrel pipets have been fabricated by a laser puller with new pulling programs and have been used to support submicro- and nanometer dual liquid/liquid interfaces. The smallest pipet that can be made by this approach is ∼20 nm in radius. These pipets have been characterized by cyclic voltammetry and scanning electron microscopy. Generation/collection mode of charge-transfer reaction is demonstrated at the submicro- and nanometer dual-liquid/liquid interfaces. The dependence of collection efficiency upon geometric parameters of the pipets has been discussed. Among the micro-, submicro-, and nanopipets, we have found that the submicro-double-barrel pipets have higher collection efficiencies than that of others and are also very close to the values predicted by the theory. Therefore, in terms of G/C mode applications, the optimal size of double-barrel pipets should be in submicrometer scale. As one of the examples of special application, we have also demonstrated that in the case of no supporting electrolyte, only the nanometer double-barrel pipets can provide reasonably good G/C results. [ABSTRACT FROM AUTHOR]

Chemical imaging analysis holds great potential in probing the chemical heterogeneity of samples with high spatial resolution and molecular specificity. This paper demonstrates the implementation of Raman mapping for microscopic characterization of tablets containing chloramphenicol palmitate polymorphs with the aid of a new multivariate image segmentation approach based on spatial directed agglomeration clustering. This approach performs the agglomeration clustering by stepwise merging the pixels possessing both spatial closeness and spectral similarity into clusters that define the image segmentation. The incorporation of spatial closeness into the clustering process enables the approach to improve the robustness and avoid poorly defined image segmentation arising from clusters with highly separated pixels. Additionally, the stepwise merging of clusters offers an F-statistic-based procedure to automatically ascertain the number of image segments. Raman mapping analysis of tablets containing two polymorphs of chloramphenicol palmitate followed by multivariate image segmentation reveals that the proposed technique offers the identification of each polymorph and a quantitative visualization of the spatial distribution of the polymorphs identified. This technique holds promise in rapid, noninvasive, and quantitative polymorph analysis for pharmaceutical production processes. [ABSTRACT FROM AUTHOR]

Describes the synthesis and application of lipophilic porphyrin dimer for mercury ions optical fiber chemical sensor. Advantages of optochemical sensors; Principles of operation of the chemical sensors; Effect of sodium tetraphenylborate on optode membrane.

Focuses on the proposal of an amperometric immunosensor for the determination of Schistosoma japonicum antibody in rabbit serum. Description of Schistosoma japonicum; Determination of the horseradish peroxidase amount fixed on the sensor surface through amperometry; Use of a paraffingraphite Schistosoma japonicum antigen biocomposite.