Determination of Single Stranded DNA using gold nanoparticle as a label by Photo Thermal Lens Microscopy in Microfluidic Chip

DNA analysis is one area that is highly suited to the microfluidic technique due to limited biological sample size and a demand for high speed and throughput [1,2]. In this regard, Photo thermal lens microscopy (PTLM) is a powerful optical detection technique that can be used in microfluidic techniques [3,4]. In the present study, detection of single-stranded deoxy ribonucleic acid (ssDNA) in microfluidic chip using nonspecific adsorption of DNAs to gold nanoparticles, is considered. The ssDNA is sufficiently flexible to partially uncoil its bases, they can be exposed to the gold nanoparticles. Under these conditions, the negative charge on the backbone is sufficiently distant so that attractive van der Waals forces between the bases and the gold nanoparticles are sufficient to cause ssDNA to stick to the gold nanoparticles and effectively prevent nanoparticles from salt-induced aggregation [5]. There is a relationship between ssDNA concentration and the effect of salt-induced aggregation of AuNPs on the PTLM signal. Thus, this relationship can be used for ssDNA detection in the channel of microfluidic chip.Herein, we developed Microchip-PTLM method for ssDNA detection in microfluidic chip. The used PTLM setup, microchip were designed, constructed and optimised in our lab. In order to evaluate performance of the present method, two types of ssDNAs are considered. Under optimum conditions, PTLM intensity of AuNPs increased with ssDNA concentration linearly. The linear responses for ssDNA I and II in a concentration range from 20 to 350 ×10-9 mol L−1 are obtained with a detection limit of 14×10-9 mol L−1 for ssDNA I and 9 ×10 -9 mol L−1 for ssDNA II. The relative standard deviations (n=8) for both ssDNAs are about 3.6%.