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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]

The existing isothermal polymerization-based signal amplification assays are usually accomplished via two strategies rolling circle amplification (RCA) and circular strand-displacement polymerization. In essence, the two techniques are based on cyclical nueclic acid strand-displacement polymerization (CNDP), limiting the application of isothermal polymerization in medical diagnosis and bioanalysis. In the present study, circular common target molecule (non-nucleic acid strand)-displacement polymerization (CCDP) is developed to amplify the fluorescence signal for biomolecule assays, extending isothermal polymerization to an aptamenc system without any medium. Via combining an aptamer with a common hairpin DNA probe, we designed a selt-blocked tluoresceflt bifunctional oligonudeotide probe (signaling probe) for the homogeneous parallel detection of two disease markers, PDGF-BB and the p53 gene. On the basis of CNDP and CCDP signal amplification, highly sensitive (e.g., detecting PDGF down to the concentration level of 1.8 x 10-10 M) and selective detection (no interference even in the presence of a significantly higher concentration (7-200 times) of nontarget proteins) was accomplished, and the linear response range was considerably widened. Furthermore, the bifunctional signaling probe exhibits impressive simplicity, convenience, and short detection time. Herein, the design of the signaling probe was described, factors influencing fluorescence signal were investigated, analytical properties were characterized in detail, and the assay application in a complex medium was validated. The proposed biosensing scheme ass proof of concept is expected to promote the application of oligonucleotide probes in basic research and medical diagnosis. [ABSTRACT FROM AUTHOR]

Aptamer-based fluorescence anisotropy (FA) assays have attracted great interest in recent years. However, a key factor that determines FA value is molar mass, thus limiting the utility of this assay for the detection of small molecules. To solve this problem, streptavidin, as a molar mass amplifier, was used in a hybridization chain reaction (HCR) to construct a target-triggered cyclic assembly of DNA–protein hybrid nanowires for highly sensitive detection of small molecules by fluorescence anisotropy. In this assay, one blocking DNA strand is released by target–aptamer recognition. The DNA then serves as an initiator to trigger enzyme-free autonomous cross-opening of hairpin probes via HCR to form a DNA nanowire for further assembly of streptavidin. Using adenosine triphosphate (ATP) as the small molecule target, this novel dual-amplified, aptamer-based FA assay affords high sensitivity with a detection limit of 100 nM. This limit of detection (LOD) is much lower than that of the disassembly approach without HCR amplification or the assembly strategy without streptavidin. In contrast to the previous turn-off disassembly approaches based on nonspecific interactions between the aptamer probe and amplification moieties, the proposed aptamer-based FA assay method exhibits a turn-on response to ATP, which can increase sensing reliability and reduce the risk of false hits. Moreover, because of its resistance to environmental interferences, this FA assay has been successfully applied for direct detection of 0.5 μM ATP in complex biological samples, including cell media, human urine, and human serum, demonstrating its practicality in real complex biological systems. [ABSTRACT FROM AUTHOR]

H2S is the third endogenously generated gaseous signaling compound and has also been known to involve a variety of physiological processes. To better understand its physiological and pathological functions, efficient methods for monitoring of H2S in living systems are desired. Although quite a few one photon fluorescence probes have been reported for H2S, two-photon (TP) probes are more favorable for intracellular imaging. In this work, by employing a donor-π-acceptor-structured naphthalene derivative as the two-photon fluorophore and an azide group as the recognition unit, we reported a new two-photon bioimaging probe 6-(benzo[d]thiazol-2'-yl)-2-azidonaphthalene (NHS1) for H2S with improved sensitivity. The probe shows very low background fluorescence in the absence of H2S. In the presence of H2S, however, a significant enhancement for both one photon and TP excited fluorescence were observed, resulting in a high sensitivity to H2S in aqueous solutions with a detection limit of 20 nM observed, much lower than the previously reported TP probe. The probe also exhibits a wide linear response concentration range (0-5 µM) to H2S with high selectivity. All these features are favorable for direct monitoring of H2S in complex biological samples. It was then applied for direct TP imaging of H2S in living cells with satisfactory sensitivity, demonstrating its value of practical application in biological systems. [ABSTRACT FROM AUTHOR]

It is well-known that Zr4+ could selectively bind with two phosphate-functionalized molecules through a coordinate covalent interaction to form a sandwich-structured complex (-PO32--Zr4+-PO32--). In this paper, we for the first time converted such interaction into fluorescence sensing systems for Zr4+ via a target-triggered DNA molecular beacon strategy. In the new designed sensing system, two phosphorylated and pyrene-labeled oligonucleotides were chosen as both recognition and reporter units, which will be linked by target Zr4+ to form a hairpin structure and bring the two labeled pyrene molecules into close proximity, resulting in a "turn-on" excimer fluorescence signal. Moreover, γ-cyclodextrin was introduced to afford an amplified fluorescence signal and, therefore, provided an improved sensitivity for the target Zr4+. This allows detection of Zr4+ with high sensitivity (limit of detection, LOD = 200 nM) and excellent selectivity. The proposed sensing system has also been used for detection of Zr4+ in river water samples with satisfactory result. [ABSTRACT FROM AUTHOR]

Fluorescence catalytic beacons have emerged as a general platform for sensing applications. However, almost all such sensing systems need covalent modification of the DNAzymes with fluorophore-quencher pairs, which may require elaborate design of the synthetic routes and many heavy and complicated synthetic steps and result in increased cost and lower synthesis yield. Here we report the construction of fluorescent cascadic catalytic beacons. With separation of the molecular recognition module from the signal reporter, this new design both avoids DNAzyme modifications and improves sensitivity through an endonuclease-based cascadic enzymatic signal amplification. This allows detection of l-histidine with high sensitivity (LOD = 200 nM) and excellent specificity. The proposed sensing system has also been used for detection of l-histidine in cellular homogenate with satisfactory results. [ABSTRACT FROM AUTHOR]

On the basis of the remarkable difference in affinity of graphene (GO) with ssDNA containing a different number of bases in length, we for the first time report a GO-DNAzyme based biosensor for amplified fluorescence "turn-on' detection of Pb2+ A FAM-labeled DNAzyme—substrate hybrid acted as both a molecular recognition module and signal reporter and GO as a superquencher. By taking advantage of the super fluorescence quenching efficiency of GO, our proposed biosensor exhibits a high sensitivity toward the target with a detection limit of 300 pM for Pb2+, which is lower than previously reported for catalytic beacons. Moreover, with the choice of a classic Pb2+-dependent GR-S DNAzyme instead of S-17 DNAzyme as the catalytic unit, the newly designed sensing system also shows an obviously improved selectivity than previously reported methods. Moreover, the sensing system was used for the determination of Pb2+ in river water samples with satisfying results. [ABSTRACT FROM AUTHOR]

This work reports the development of a new molecular beacon-based junction sensing system with highly Sensitive DNA detection and a strong capability to identify SNPs. The single linear probe typically labels the midsection of the oligonucleotide, but our next-generation junction sensing system uses a hairpin-structured MB with labels on each end of the oligonucleotide to maintain the cleaving activity of our newly designed ssDNA-cleaved endonuclease, Nt.BbvCI, rather than the typical dsDNAcleaved endonuclease. These design improvements guarantee a true and efficient target-triggered enzymatic recycling amplification process in our sensing system. They also afford a faster and more sensitive response toward target DNA than the first-generation junction sensing system. [ABSTRACT FROM AUTHOR]

Mesoporous SBA-15 silica is an excellent support for constructing fluorescent surface sensors. In this letter, we reported a two-step surface reaction involved strategy to construct efficient fluorescent surface sensors for metal ions by clicking fluoroionophores onto azide-functionalized SBA-15. Our experimental results indicate that such a strategy exhibits an obviously higher loading efficiency within commercial SBA-15 than a previously reported strategy. As a proof-of-concept, a newly designed alkyne-functionalized Hg2+ fluoroionophore was grafted onto SBA-15 to form a fluorescent Hg2+ surface sensor. It shows improved sensitivity and selectivity than the fluoroionophore itself working in the solution phase with a detection limit of 2.0 x 10-8 M for Hg2+. [ABSTRACT FROM AUTHOR]

This letter described the design and synthesis of a novel fluorescein-appended rhodamine spirolactam derivative and its preliminary application as a ratiometjic fluorescent cellular imaging probe for Zn2+. The ratiometric fluorescent signal change of the probe is based on an intramolecular fluorescence resonance energy transfer (FRET) mechanism modulated by a specific metal ion induced ring-opening process of the rhodamine spirolactam (acting as a trier). in the new developed sensing system, the emission peaks of the two fluomphores are well-resolved, which can avoid the emission spectra overlap problem generally met by spectra-shift type probes and benefits for observation of fluorescence signal change at two different emission wavelengths with high resolution. It also benefits for a large range of emission ratios, thereby a high sensitivity for Zn2+-detection. Under optimized experimental conditions, the probe exhibits a stable response for Zn2+ over a concentration range from 2.0 x 10-7 to 2.0 x 10-5 M, with a detection limit of 4.0 x 10-8 M. Most importantly, the novel probe has well solved the problem of serious interferences from other transition metal ions generally met by previously reported typical fluorescent probes for Zn2+ with the di(2-picolyl)amine moiety as the receptor (in this case, the fluorescence response induced by Cd2+ is even comparable to that of Zn2+) and shows a reversible and fast response toward Zn2+. All these unique features make it particularly favorable for ratiometric cellular imaging investigations. It has been preliminarily used for ratiometric imaging of Zn2+ in living cells with satisfying resolution. [ABSTRACT FROM AUTHOR]

A universal approach is proposed in this study for the development of an aptameric assay system for proteins based on aptamer structure-switching-triggered ligationrolling circle amplification (I,RCA) upon target binding. The strategy chiefly depends on the competition for binding the aptamer probe between target protein and a complementary single-stranded DNA (CDNA) that can induce the circularization of the padlock probe. Introduction of target protein into the assay system inhibits the hybridization of the CDNA with the aptamer probe because of the formation of the target/aptamer duplex. The free CDNA can only hybridize with the padlock probe. With the assistance of DNA ligase, the padlock probe is circularized, and the subsequent RCA process can be accomplished by Phi 29 DNA polymerase. Each RCA product containing thousands of repeated sequences might hybridize with a large number of molecular beacons (detection probes), resulting in an enhanced fluorescence signal. In contrast, in the absence of target protein, no obvious change in the fluorescence intensity of the detection probe is observed. This signaling mode for target recognition and transduction events is based on the combination of aptamer recognition elements and L-RCA technology with high specificity and sensitivity. The proposed assay system not only exhibits excellent analytical characteristics (e.g., the detection limit on attomolar scale and a linear dynamic range of more than 3 orders of magnitude) but also possesses significant advantages over existing aptameric assays. The proposed strategy is universal since the sequences of aptamer probe, CDNA, and padlock probe could be easily designed to be compatible with the L-RCA based detection of other proteins without other conditions. [ABSTRACT FROM AUTHOR]

A new fluorescence method based on aptamer-target interactions has been developed for cocaine detection with target-induced strand displacement Here we describe new probes, the hairpin-probe and the single strand-probe (ss-probe), that possess two recognition sequences of cocaine aptamer. In the presence of cocaine, both probes would associate with the target to form a tripartite complex. The conformational change in the hairpin-probe causes the opening of a hairpin structure and the hybridization to primer. With polymerase and the dNTPs, the replication of the single-stranded domain of hairpin-probe triggers the process of primer extension. When the hairpin-probe is converted into a fully double stranded form, the ss-probe and cocaine are displaced to bind another hairpin-probe and initiate new amplification cycles. Fluorescence signal generation would be observed upon SYBR Green I intercalating into the new DNA double helix. The new protocol design permits detection of as low as 2 nM cocaine in a closed tube, offering a convenient approach for a homogeneous assay. Compared with previously reported cocaine aptameric sensors, our new method is highly sensitive, selective, and economical. [ABSTRACT FROM AUTHOR]

We have developed an electrostatic interaction based biosensor for thrombin detection using surface-enhanced Raman spectroscopy (SERS). This method utilized the electrostatic interaction between capture (thrombin aptamer) and probe (crystal violet, CV) molecules. The specific interaction between thrombin and aptamer could weaken the electrostatic barrier effect from the negative charged aptamer SAMs to the diffusion process of the positively charged CV from the bulk solution to the Au nanoparticle surface. Therefore, the more the bound thrombin, the more the CV molecules near the Au nanoparticle surface and the stronger the observed Raman signal of CV, provided the Raman detections were set at the same time point for each case. This procedure presented a highly specific selectivity and a linear detection of thrombin in the range from 0.1 nM to 10 nM with a detection limit of about 20 pM and realized the thrombin detection in human blood serum solution directly. The electrostatic interaction based technique provides an easy and fast-responding optical platform for a "signal-on" detection of proteins, which might be applicable for the real lime assay of proteins. [ABSTRACT FROM AUTHOR]

In this paper, we unveil a novel naphthalimide—porphyrin hybrid based fluorescence probe (1) for ratiometric detection of Hg2+ in aqueous solution and living cells. The ratiometric signal change of the probe is based on a carefully predesigned molecule containing two independent Hg2+-sensitive fluorophores with their maximal excitation wavelengths located at the same range, which shows reversibly specific ratiometric fluorescence responses induced by Hg2+. In the new developed sensing system, the emissions of the two fluorophores are well-resolved with a 125 nm difference between two emission maxima, which can avoid the emission spectra overlap problem generally met by spectra-shift type probes and is especially favorable for ratiometric imaging intracellular Hg2+. It also benefits from a large range of emission ratios and thereby a high sensitivity for Hg2+-detection. Under optimized experimental conditions, the probe exhibits a stable response for Hg2+ over a concentration range from 1.0 x 10-7 to 5.0 x 10-5 M, with a detection limit of 2.0 x 10-8 M. The response of the probe toward Hg2+ is reversible and fast (response time less than 2 min). Most importantly, the ratiometric fluorescence changes of the probe are remarkably specific for Hg2+ in the presence of other abundant cellular metal ions (i.e., Na+, K+, Mg2+, and Ca2+), essential transition metal ions in celsl (such as Zn2+, Fe3+, Fe2+, Cu2+, Mn2+, Co2+, and Ni2t), and environmentally relevant heavy metal ions (Ag, Pb2+, Cr3+, and Cd2+), which meets the selective requirements for biomedical and environmental monitoring application. The recovery test of Hg2+ in real water samples demonstrates the feasibility of the designed sensing system for Hg3+ assay in practical samples. It has also been used for ratiometiic imaging of Hg2+ in living cells with satisfying resolution, which indicates that our novel designed probe has effectively avoided the general emission spectra overlap problem of other ratiometric probes. [ABSTRACT FROM AUTHOR]

The development of ultrasensitive and rapid methods for the detection of dipicolinic acid (DPA), a biomarker for bacterial spores including Bacillus anthracis, is increasingly important. This paper reports the results of an investigation of surface enhanced Rasnan spectroscopy (SEllS) based ultrasensitive detection of DPA using a gold nanoparticle/polyvinylpyrrolidone/gold substrate (AuNPs/ PVP/Au). The strong SERS effect of this substrate exploits the particle-particle and particle-substrate plasmonic coupling, which is optimized by manipulating the diameter of the nanoparticles (50-70 nm). The correlation between the SERS intensity of the diagnostic band and the DPA concentration (0.1 ppb to 100 ppm) was shown to exhibit two linear regions, i.e., the low-(<0.01 ppm) and high-concentration (>1 ppm) regions, with an intermediate region in between. The presence of a linear relationship in the low-concentration region was observed for the first time in SEllS detection of DPA. A detection limit of 0.1 ppb was obtained from the substrates with 60 nm sized Au NPs, which is, to our knowledge, the lowest detection limit reported for DPA using this type of SERS substrate. This finding was also supported by the estimated enhancement factor (∼106) and a large adsorption equilibrium constant for the low-concentration region (1.7 x 107 M-1). The adsorption characteristics of DPA on the SERS substrates were analyzed in terms of monolayer and multilayer adsorption isotherms to gain insights into the correlation between the SEllS intensity and the DPA concentration. The observed transition from the low- to high-concentration linear regions was found to correspond to the transition from a monolayer to multilayer adsorption isotherm, which was in agreement with the esthnated minimum DPA concentration for a monolayer coverage (∼0.01 ppm). [ABSTRACT FROM AUTHOR]

A novel rolling circle amplification (RCA) immunoassay based on DNA-encapsulating liposomes, liposome-RCA immunoassay, was developed for ultrasensitive protein detection. This technique utilized antibody-modified liposomes with DNA prime probes encapsulated as the detection reagent in the sandwiched immunoassays. The DNA prime probes were released from liposomes and then initiated a linear RCA reaction, generating a long tandem repeated sequences that could be selectively and sensitively detected by a microbead-based fluorescence assay. The developed technique offered very high sensitivity due to primary amplification via releasing numerous DNA primers from a liposome followed by a secondary RCA amplification. A biobarcode design was incorporated in the technique, which allowed the strategy to be directly implemented for multiplex assay of multiple proteins. Also, the technique allowed easy preparation of the DNA-carrying antibody reagent and the implementation with simple instrumentation. The technique was demonstrated for the determination of prostate-specific antigen (PSA), a highly selective biomarker associated with prostate cancer. The results revealed that the technique exhibited a dynamic response to PSA over a 6-decade concentration range from 0.1 fg mL-1 to 0.1 ng mL-1 with a limit of detection as low as 0.08 fg mL-1 and a high dose-response sensitivity. The liposome-RCA immunoassay holds great promise as a versatile, sensitive, and robust platform to combine the nucleic acid amplification with immunoassay for ultrasensitive protein detection. [ABSTRACT FROM AUTHOR]

The design and synthesis of a novel rhodamine spirolactam derivative and its application in fluorescent detections of Cu2+in aqueous solution and living cells are reported. The signal change of the chemosensor is based on a specific metal ion induced reversible ring-opening mechanism of the rhodamine spirolactam. It exhibits a highly sensitive "turn-on" fluorescent response to- ward Cu2+ in aqueous solution with an 80-fold fluorescence intensity enhancement under 10 equiv of Cu2+ added. This indicates that the synthesized chemosensor effectively avoided the fluorescence quenching for the paramagnetic nature of Cu2+ via its strong binding capability toward Cu2+. With the experimental conditions optimized, the probe exhibits a dynamic response range for Cu2+ from 8.0 × 107 to 1.0 × 105 M, with a detection limit of 3.0 × 107 M. The response of the chemosensor for Cu2+ is instantaneous and reversible. Most importantly, both the color and fluorescence changes of the chemosensor are remarkably specific for Cu2+ in the presence of other heavy and transition metal ions (even those that exist in high concentration), which meet the selective requirements for biomedical and environmental monitoring application. The proposed chemosensor has been used for direct measurement of Cu2+ content in river water samples and imaging of Cu2+ in living cells with satisfying results, which further demonstrates its value of practical applications in environmental and biological systems. [ABSTRACT FROM AUTHOR]

A novel electrochemical sensor was developed for sensitive and selective detection of mercury(II), based on thymine-Hg2+-thymine (T-Hg2+-T) coordination diemistiy. This strategy exploited the cooperativity of proximate poly-T oligonucleotides in coordination with Hg2+. Ferrocene (Fc)-tagged poly-T oligonucleotides were immobilized on the electrode surface via self-assembly of the terminal thiol moiety. In the presence of Hg2+, a pair of poly-T oligonucleotides could cooperatively coordinate with Hg2+, which triggered a conformational reorganization of the poly-T oligonucleotides from flexible single strands to relatively rigid duplex like complexes, thus drawing the Fe 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 Hg2+ in a concentration range from 1.0 nM to 2.0 μM, with a detection limit of 0.5 nM. Also, this strategy afforded exquisite selectivity for Hg2+ 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 Hg2+ detection. [ABSTRACT FROM AUTHOR]

This paper describes a novel electrochemical DNA (E-DNA) biosensor for simple, rapid, and specific detection of nucleic acids based on the proximity-dependent surface hybridization assay. This E-DNA biosensor was constructed by self-assembly of a 3' short thiolated capture probe on the gold electrode. DNA detection was realized by outputting a remarkable redox current of the 5' ferrocene (Fc) tail labeled probe. When the target DNA was introduced into the system, it was complementary to the 5' Fc labeled probe at the one-half-segment and complementary to the 3' short thiolated capture probe at the other half-segment, resulting in forming a stable duplex complex. As a result, the Fc probe was proximate to the electrode surface, and the Faradaic current was observed. This E-DNA biosensor was proved to have a low detection limit (1 fM) and a wide dynamic range (from 1 fM to 1 nM) due to the stable hybridization mode. In addition, the sensing system could discriminate the complementary sequence from mismatch sequences, with high sensitivity, stability, and reusability. [ABSTRACT FROM AUTHOR]

We have developed an electrostatic interaction based biosensor for thrombin detection using surface-enhanced Raman spectroscopy (SERS). This method utilized the electrostatic interaction between capture (thrombin aptamer) and probe (crystal violet, CV) molecules. The specific interaction between thrombin and aptamer could weaken the electrostatic barrier effect from the negative charged aptamer SAMs to the diffusion process of the positively charged CV from the bulk solution to the Au nanoparticle surface. Therefore, the more the bound thrombin, the more the CV molecules near the Au nanoparticle surface and the stronger the observed Raman signal of CV, provided the Raman detections were set at the same time point for each case. This procedure presented a highly specific selectivity and a linear detection of thrombin in the range from 0.1 nM to 10 nM with a detection limit of about 20 pM and realized the thrombin detection in human blood serum solution directly. The electrostatic interaction based technique provides an easy and fastresponding optical platform for a "signal-on" detection of proteins, which might be applicable for the real time assay of proteins. [ABSTRACT FROM AUTHOR]

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 ultrasensilive immunoassay. [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.

Fluorescence resonance energy transfer (FRET) strategy has been widely applied in designing ratiometric probes for bioimaging applications. Unfortunately, for FRET systems, sufficiently large spectral overlap is necessary between the donor emission and the acceptor absorption, which would limit the resolution of double-channel images. The through-bond energy transfer (TBET) system does not need spectral overlap between donor and acceptor and could afford large wavelength difference between the two emissions with improved imaging resolution and higher energy transfer efficiency than that of the classical FRET system. It seems to be more favorable for designing ratiometric probes for bioimaging applications. In this paper, we have designed and synthesized a coumarin- rhodamine (CR) TBET system and demonstrated that TBET is a convenient strategy to design an efficient ratiometric fluorescent bioimaging probe for metal ions. Such TBET strategy is also universal, since no spectral overlap between the donor and the acceptor is necessary, and many more dye pairs than that of FRET could be chosen for probe design. As a proof-of-concept, Hg2+ was chosen as a model metal ion. By combining TBET strategy with dual-switch design, the proposed sensing platform shows two well- separated emission peaks with a wavelength difference of 110 nm, high energy transfer efficiency, and a large signal-to-background ratio, which affords a high sensitivity for the probe with a detection limit of 7 nM for Hg2+. Moreover, by employing an Hg2+-promoted desulfurization reaction as recognition unit, the probe also shows a high selectivity to Hg2+. All these unique features make it particularly favorable for ratiometric Hg2+ sensing and bioimaging applications. It has been preliminarily used for a ratiometric image of Hg2+ in living cells and practical detection of Hg2+ in river water samples with satisfying results. [ABSTRACT FROM AUTHOR]