Herein, we report the construction of a colorimetric probe used to detecting Cr 3+ ions in aqueous solution based on functionalized gold nanoparticles. We investigated 4-mercaptobenzoic acid, 4-nitrobenzenethiol, and a mixture of 4-mercaptobenzoic acid and 4-nitrobenzenethiol as ligands for Cr 3+ ions to functionalize the gold nanoparticles, respectively. The results showed that the three probes were all aggregated in the presence of Cr 3+ ions, which induces a color change from ruby to violet. Moreover, gold nanoparticles modified with 4-mercaptobenzoic acid exhibit a higher response toward Cr 3+ than the two other probes, which can be detected by the naked eye and UV-vis absorption spectroscopy. The detection time was rapid (within 25 min). A linear relationship was obtained from 20 to 25 μM between the ratio of the absorbance observed at 635 nm and 520 nm (A635 nm/A520 nm) with the limit of detection was 5 × 10 −6 M. This method exhibited excellent selectivity for Cr 3+ ions over other tested heavy metal ions, anions, and organic molecules in the absence of another shielding reagent of metal ion. The system was successfully utilized to detect Cr 3+ ions in simulated samples.

Nucleic acid detection is becoming increasingly important in the diagnostics of genetic diseases for biological analysis. We herein propose gold nanoparticles as probe for colorimetric detection of nucleic acids with branched DNA nanostructures, which enables a novel and simple colorimetric biosensor. In our system, the target DNA specifically triggered two short-chain ssDNA probes to generate branched DNA nanostructures (Y-shape DNA), which prevent AuNPs from aggregation in aqueous NaCl solution. On the contrary, when the target DNA did not exist, gold nanoparticles were unstable and aggregated easily because there is no anti-aggregation function from Y-shape DNA. Sensor response was found to be proportional to the target DNA concentration from 5 to 100[Formula: see text]nM, with detection limits determined as 5[Formula: see text]nM. The developed platform is for colorimetric nucleic acid detection without enzymes, label and modification holds great promise for practical applications.

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