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Here, a simple, and highly sensitive fluorescent assay is designed to monitor K + . The versatile, robust biosensing strategy is based on the specific recognition utility of label-free aptamers with their targets and PicoGreen dye as the signal probe. The aptamers undergo a conformational change to a secondary structure such as G-quadruplex in the presence of targets. In addition to a conformational change with its targets, the remaining single-stranded DNA (ssDNA) aptamer form a duplex structure with its complete complementary sequence. Conformational changes of aptamers as well as fluorescence amplification produce clear signal-off in the presence of targets. Fluorescent assay employing this mechanism for the detection of K + is highly sensitive, and selective. The detection limit of the K + assay is determined to be 2.37 pM. The sensing strategy is low-cost and simple in its operation without requirement for complex labeling of probe DNA or sophisticated synthesis of the fluorescent compound. Also, the method has less structural requirement of complexes of aptamers with their targets, thus rending its wilder applications for various targets. [ABSTRACT FROM AUTHOR]

Herein, a label-free and highly sensitive electrochemical aptasensor for the detection of angiogenin was proposed based on a conformational change of aptamer and amplification by poly(diallyldimethyl ammonium chloride) (PDDA)-functionalized graphene/gold nanoparticles (AuNPs) composites-modified electrode. PDDA-functionalized graphene (P-GR) nanosheets as the building block in the self-assembly of GR nanosheets/AuNPs heterostructure enhanced the electrochemical detection performance. The electrochemical aptasensor has an extraordinarily sensitive response to angiogenin in a linear range from 0.1 pM to 5 nM with a detection limit of 0.064 pM. The developed sensor provides a promising strategy for the cancer diagnosis in medical application in the future. [ABSTRACT FROM AUTHOR]

Abstract: A colorimetric assay for the ultrasensitive determination of thrombin based on cationic polymer and gold nanoparticles was presented, in which unmodified gold nanoparticles (AuNPs) was used as probes and 21-mer thrombin-binding aptamer (TBA) as sensing elements. Upon the addition of thrombin, TBA interacted specifically with thrombin to form a G-quadruplex structure. As a result, the conformation change facilitated the cationic polymer, poly(diallyldimethylammonium chloride) (PDDA)-induced AuNP aggregation. Thus, the visible change in color from wine-red to blue–purple was readily seen by the naked eye. The colorimetric sensor could detect thrombin down to 1pM with high selectivity in the presence of other interferring proteins. Furthermore, the assay was successfully employed to determine thrombin in human serum sample, which suggested its great potential for diagnostic purposes. [Copyright &y& Elsevier]

Abstract: Herein, a label-free and highly sensitive electrochemical impedance spectroscopy (EIS) aptasensor for the detection of potassium ion (K+) was developed based on a conformational change in which a K+-stabilized single stranded DNA (ssDNA) with G-rich sequence was used as the recognition element. In the measurement of K+ ions, the change in interfacial electron transfer resistance (R ct) of the sensor using a redox couple of [Fe(CN)6]3−/4− as the probe was monitored. In the presence of K+, the G-rich DNA folded into the G-quadruplex structure, and then K+ can bind to the G-quadruplex structure, leading to an increase in the R ct. The R ct increased with K+ concentration, and the plot of R ct against the logarithm of K+ concentration is linear over the range from 0.1nM to 1mM with a detection limit of 0.1nM. Other metal ions, such as Ca2+, Mg2+, Na+, Li+, Al3+, Zn2+, Cu2+, and Ni2+ caused no notable interference on the detection of K+. The scheme reported herein is applicable to the detection of other kinds of G-rich aptamer-binding chemicals and biomolecules. [Copyright &y& Elsevier]

Highlights: [•] A simple and novel colorimetric method for detection of K+ was developed. [•] The aptasensor exhibited low detection limit and wide linear range to K+. [•] This method was able to detect K+ with high selectivity. [•] This colorimetric method exhibited excellent applicability. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we described signal amplification architecture for electronic aptamer-based sensor (E-AB), which is applicable to a wide range of aptamers. Herein, we only take lysozyme as the representative sensing target. The amplification method was based on the network of thiocyanuric acid (TCA)/gold nanoparticles (AuNPs) modified with ssDNA. The binding event can be detected by a decrease in the integrated charge of the surface-bound [Ru(NH3)6]3+ which electrostatically absorbed onto the negatively charged phosphate backbones of DNA. In the presence of target molecules, a large amount of TCA/AuNP/ssDNA network associated with [Ru(NH3)6]3+ would be removed from the electrode surface, leading to a significant decrease of redox current. Cyclic voltammetry (CV) signals of [Ru(NH3)6]3+ provides quantitative measures of the concentrations of lysozyme, with a linear calibration ranging from 5pM to 1nM and a detection limit is 0.1pM. The detection limit of the proposed sensor is one order of magnitude and three orders of magnitude more sensitive than the detection limits in the absence of TCA (5pM) and in the absence of TCA/AuNP/ssDNA network (0.5nM). This amplification method is promising for broad potential application in clinic assay and various protein analysis. [Copyright &y& Elsevier]

Abstract: A simple, highly sensitive, and label-free electrochemical impedance spectroscopy (EIS) aptasensor based on an anti-lysozyme-aptamer as a molecular recognition element, was developed for the detection of lysozyme. Improvement in sensitivity was achieved by utilizing gold nanoparticles (AuNPs), which were electrodeposited onto the surface of a gold electrode, as a platform for immobilization of the aptamer. To quantify the amount of lysozyme, changes in the interfacial electron transfer resistance (R et) of the aptasensor were monitored using the redox couple of an [Fe(CN)6]3−/4− probe. The R et increased with lysozyme concentration. The plot of R et against the logarithm of lysozyme concentration is linear over the range from 0.1pM to 500pM with a detection limit of 0.01pM. The aptasensor also showed good selectivity for lysozyme without being affected by the presence of other proteins. [ABSTRACT FROM AUTHOR]

Abstract: A one-step electrochemical sensor for sensing of potassium ion (K+) based on the conformational change of a single stranded DNA (ssDNA) with G-rich sequence was presented. The introduction of K+ induced folding of the aptamer, and the Fc moiety approached the electrode surface to produce measurable electrochemical signals. The aptasensor had a lower detection limit at 0.1nM, which was an excellent sensitivity compared with other methods for K+ detection. The proposed approach showed high selectivity and minimized the nonspecific adsorption, so that it was used for the detection of target K+ in the human serum sample. [Copyright &y& Elsevier]

Abstract: Angiogenin (Ang), one of the most potent angiogenic factor, is related with the growth and metastasis of numerous tumors. This paper presents a very simple and label-free square-wave voltammetry (SWV) aptasensor to detect angiogenin, in which an anti-angiogenin-aptamer was used as a molecular recognition element, and the couple ferro/ferricyanide as a redox probe. At the bare gold electrode, the redox couple (K4[Fe(CN)6]/K3[Fe(CN)6]) can be very easily accessed to the electrode surface to give a very strong SWV signal. At the anti-angiogenin/Au electrode surface, when angiogenin was added to the electrochemical cell, the binding of the analyte results in less availability for a redox reaction, which led to smaller SWV current. To quantify the amount of angiogenin, current suppressions of SWV peak were monitored using the redox couple of an [Fe(CN)6]4−/3− probe. The plot of signal suppression against the logarithm of angiogenin concentration is linear with over the range from 0.01nM to 30nM with a detection limit of 1pM. The aptasensor also showed very good selectivity for angiogenin without being affected by the presence of other proteins in serum. It is the first time to use a very simple method to detect the cancer marker. Such an aptasensor opens a rapid, selective and sensitive route for angiogenin detection and provides a promising strategy for other protein detections. [Copyright &y& Elsevier]

[Display omitted] • Ultrasensitive detection of adenosine is realized based on three-dimensional Au/TiO 2 nanorod arrays. • The TiO 2 nanorod arrays grown on FTO substrate can attach a large number of Au nanoparticles. • Among these five Au/TiO 2 nanorod arrays, the sensing performance of Au/TiO 2 -(0.65)-nanorod array is the best. • The aptasensor showed good accuracy, excellent selectivity, superb stability, and good application in serum. An electrochemical aptasensor was constructed based on Au/TiO 2 nanorod arrays for ultrasensitive detection of adenosine. Specifically, The TiO 2 nanorod arrays grown on FTO substrate can attach a large number of Au nanoparticles (AuNPs), which greatly increase the immobilization of aptamers and significantly improve the redox signal of electrostatically adsorbed [Ru(NH 3) 6 ]3+. In the presence of adenosine, the number of [Ru(NH 3) 6 ]3+ electrostatically adsorbed on the aptamer skeleton decreases, resulting in a decline in the detected square wave voltammetry (SWV) signal. Under the optimal conditions, the peak SWV current values of aptasensor based on five TiO 2 nanorod arrays are linear with the logarithmic concentration of adenosine, and the minimum detection limit is 0.42 fM. More importantly, the aptasensor has shown high specificity, extraordinary precision, continuous stability, as well as wonderful applicability for adenosine. Hence, the aptasensor paves the way for developing an effective clinical diagnostic means for adenosine detection. [ABSTRACT FROM AUTHOR]