Search

In this work, a rapid, simple and sensitive colorimetric sensor for simultaneous (or respective) detection of Cr 3 + and Pb 2 + using tyrosine functionalized gold nanoparticles (AuNPs Tyr ) has been developed. Tyrosine, a natural and zwitterionic amino acid, could be as a reducing and capping agent to synthesise AuNPs and allow for the simultaneous and selective detection of Cr 3 + and Pb 2 + . Upon the addition of Cr 3 + or Pb 2 + (a combination of them), the color of AuNPs Tyr solution changes from red to blue grey and the characteristic surface plasmon resonance (SPR) band is red-shifted to 580 nm due to the aggregation of AuNPs. Interestingly, the aggregated AuNPs Tyr can be regnerated and recycled by removing Pb 2 + and Cr 3 + . Even after 3 rounds, AuNPs Tyr show almost the same A 580 nm / A 520 nm value for the assays of Pb 2 + and Cr 3 + , indicating the good recyclability of the colorimetric sensor. The responding time (within 1 min) and sensitivity of the colorimetric sensor are largely improved after the addition of 0.1 M NaCl. Moreover, the AuNPs Tyr aggregated by Cr 3 + or Pb 2 + (a combination of them) show excellent selectivity compared to other metal ions (Cr 3 + , Pb 2 + , Fe 2 + ,Cu 2 + ,Zn 2 + ,Cr 6 + ,Ni 2 + ,Co 2 + ,Hg 2 + ,Mn 2 + ,Mg 2 + ,Ca 2 + ,Cd 2 + ). More importantly, the developed sensor manifests good stability at room temperature for 3 months, which has been successfully used to determine Cr 3 + and Pb 2 + in the real water samples with a high sensitivity. [ABSTRACT FROM AUTHOR]

A method is described for the determination of the activity of endonuclease. It based on the deaggregation of gold nanoparticles (AuNPs) aggregated by the action of poly(diallyldimethylammonium chloride) (PDDA). A single-stranded DNA (ssDNA) is released after enzymatic cleavage catalyzed by endonuclease. The released fragments bind electrostatically to PDDA and inhibit the PDDA-induced aggregation of AuNPs. This is accompanied by a color change from blue to red and a decrease in the absorption ratio (A630/A520). Under the optimal conditions, this ratio increases linearly in the 0.001 to 1 U·μL−1 EcoRI endonuclease activity range. The detection limit is of 2 × 10−4 U·μL−1 which is much better or at least comparable to previous reports. The method is deemed to have wide scope in that it may be used to study other endonuclease activity (such as BamHI) by simply changing the specific recognition site of the hairpin-like DNA probe. The assay may also be employed to screening for inhibitors of EcoRI endonuclease.Schematic presentation of the colorimetric assay based on the deaggregation of AuNPs for the detection of endonuclease activity. A single-stranded sequence (ssDNA) is released by the EcoRI cleavage, which electrostatically binds to PDDA and inhibits the PDDA-induced aggregation of AuNPs accompanying with a color change from blue to red. [ABSTRACT FROM AUTHOR]

A colorimetric method is described for the determination of Pt(II). It is based on the use of gold nanoparticles (AuNPs) which are known to aggregate in the presence of a cationic polymer such as poly(diallyldimethylammonium chloride) (PDDA). If, however, a mismatched aptamer (AA) electrostatically binds to PDDA, aggregation is prevented. Upon the addition of Pt(II), it will bind to the aptamer and induce the formation of a hairpin structure. Hence, interaction between aptamer and PDDA is suppressed and PDDA will induce the aggregation of the AuNPs. This is accompanied by a color change from red to blue. The effect can be observed with bare eyes and quantified by colorimetry via measurement of the ratio of absorbances at 610 nm and 520 nm. Response is linear in the 0.24-2 μM Pt(II) concentration range, and the detection limit is 58 nM. The assay is completed within 15 min and selective for Pt(II) even in the presence of other metal ions. It was successfully applied to the rapid determination of Pt(II) in spiked soil samples.Schematic representation of the method for detection of Pt(II) based on the use of a cationic polymer and gold nanoparticles. In the presence of Pt(II), aptamer interacts with the Pt(II) and prevents the interaction between aptamer and cationic polymer. Hence, cationic polymer induce the aggregation of the AuNPs and lead to the color change from red to blue. [ABSTRACT FROM AUTHOR]