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We have presented an extensible, facile and sensitive multidimensional sensor based on DNA-gold nanoparticle (DNA-AuNP) conjugates for heavy metal ions (Ag + , Hg 2+ , Cr 3+ , Sn 4+ , Cd 2+ , Cu 2+ , Pb 2+ , Zn 2+ , and Mn 2+ ) discrimination. In the presence of metal ions, the excluded effect of DNA and AuNPs with the same negative charges is disrupted, and the amount of FAM-labeled DNA adsorbed on AuNP surfaces increases, resulting in a more obvious fluorescence quenching effect. With the addition of NH 2 OH and HAuCl 4 , AuNPs grow into morphologically varied nanostructures (spherical to branched) depending on the resulting aptamer coverage, which gives rise to different colored solutions (reddish blush, purple and blue) observed by naked eyes. By simply changing the DNA sequences, three sensing elements can be easily obtained and added into this dual-channel multidimensional sensor. 9 heavy metal ions are distinguished by linear discriminant analysis (LDA) and primary component analysis (PCA). A highly sensitive discrimination of metal ion targets with the detection limit as low as 50 nM with 100% identification accuracy is obtained. Remarkably, Cu 2+ and Hg 2+ ions with similar catalytic performance at various concentrations (300 nM, 400 nM, 500 nM, respectively) and the mixture of the two metal ions with different volume ratios (total metal ion concentration: 500 nM) can be successfully discriminated. In addition, nine heavy metal ions are also well-distinguished in river samples, and the accuracy of discrimination of these metal ions samples reaches 100%. Therefore, it will broaden the application field of DNA-AuNP conjugates-based multidimensional sensors. [ABSTRACT FROM AUTHOR]

In this work, we report a simple, ultrasensitive, and feasible colorimetric assay for metal ion (K + , used as a model) via inherent peroxidase-like enzymatic amplification strategy of gold nanoparticles (AuNPs). It is shown that peroxidase-like activity of AuNPs can be improved dramatically by its surface activation with target-specific aptamer molecules. Whereas when the target exists, the aptamers leave the surface of AuNPs in a target concentration-dependent manner, resulting in a decrease of the nanoenzymatic catalytic ability of AuNPs. Thus, K + can be quantified in the presence of AuNPs by using a colorimetric sensing probe (3,3′,5,5′-tetramethylbenzidine). The color change of the solution is relevant to the dose of the target, and this can be achieved with the naked eyes and monitored by UV–vis spectrometry. A linear dependence between the absorbance and target K + concentration is obtained under optimal conditions in the range from 0. 1 nM to 1 μM with a detection limit (LOD) of 0.06 nM estimated at the 3S blank level . The sensitivity displays to be 2–9 orders of magnitude better than those of other K + detection methods. This sensing strategy may in principle be universally applicable for the detection of a range of environmental or biomedical molecules of interest. [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]

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: 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]

A facile colorimetric sensor array for detection of proteins was demonstrated using DNA as nonspecific receptors. We found that different proteins could trigger the DNA-protected gold nanoparticles (AuNPs) to show different aggregation behaviors in the presence of salt with high concentrations along with various color changes. As a proof-of-concept application, a multi-protein discrimination array was fabricated with two ssDNA strands (15A and 30A bases) as a receptor array. The combinatorial colorimetric response of this sensor array can be analyzed by linear discriminant analysis (LDA) and hierarchical cluster analysis (HCA). 12 proteins have been well distinguished with the naked eye at the 50 nM level. The proteins in human serum have also been discriminated. Furthermore, the accuracies of discrimination of the similar mixtures of proteins and unknown samples were all 100%. [ABSTRACT FROM AUTHOR]