A label-free and enzyme-free colorimetric sensing platform for the amplified detection of target protein was developed based on an ingenious combination of nonlinear hybridization chain reaction and a gold nanoparticle aggregation strategy. The combination of gold nanoparticles (AuNPs) with DNA has a history now spanning two decades, with potential applications in biomedicines and biosensors. Now, Prof. Chii-Wann Lin from the Institute of Biomedical Engineering and his group show a new way of using AuNPs and DNA together, taking advantage of a technique called nonlinear hybridization chain reaction (NHCR) which is the formation of dendritic nanostructures of DNA through a self-sustained, branching growth mechanism.1 Here, the researchers develop a method to control assembly of AuNPs using a similar nonlinear hybridization chain reaction technique. DNA aptamers selected to bind specific molecules hold promise for the development of NHCR triggers that will initiate the chain reaction only in the presence of the target molecule. A programmed DNA dendritic nanostructure was formed using two double-stranded substrate DNAs and two single-stranded auxiliary DNAs as assembly components via a target-assisted cascade amplification reaction, and it was then captured by DNA sensing probe-stabilized AuNPs. The release of sensing probes from AuNPs led to the formation of unstable AuNPs, promoting salt-induced aggregation. Prof. Lin and co-workers have used this aptamer trigger concept to specifically detect vascular endothelial growth factor (VEGF). The merits of the assay are that it does not require time-consuming AuNP surface modification and enzymatic amplification steps. Additionally, this assay requires less than an hour for its completion, compared with several hours for DNA-based linear amplification detection. Prof. Lin remarks, "If we succeed in developing a general aptamer triggering mechanism for biosensing, then NHCR amplification could be incorporated in sensors for a wide range of biomolecules." Also, Prof. Lin’s group currently works with mobile platforms to assist with on-site testing and health care and, thus, this technique will be applied for point-of-care quantitative detection using a smartphone-based device in the future. Colorimetric detection of VEGF using DNA sensing probe-stabilized AuNPs Reference 1 Chang, C.C., Chen, C.Y., Chuang, T.L., Wu, T.H., Wei, S.C., Liao, H., Lin, C.W., Aptamer-based colorimetric detection of proteins using a branched DNA cascade amplification strategy and unmodified gold nanoparticles. Biosensors and Bioelectronics 78, 200–205 (2016). doi: 10.1016/j.bios.2015.11.051 Reference Chia-Chen Chang, Chen-Yu Chen, Tsung-Liang Chuang, Tzu-Heng Wu, Shu-Chen Wei, Hongen Liao, Chii-Wann Lin, Aptamerbased colorimetric detection of proteins using a branched DNA cascade amplification strategy and unmodified gold nanoparticles. Biosensors and Bioelectronics 78, 200–205 (2016). DOI: 10.1016/ j.bios.2015.11.051. Professor Chii-Wann Lin Institute of Biomedical Engineering cwlinx@ntu.edu.tw