Simple colorimetric detection of dopamine using modified silver nanoparticles

Dopamine （DA） plays an important role in health and peripheral nervous systems. Colorimetric detection of DA has the ad- vantage of color change and simplicity in operation and instrumentation. Herein, we report a highly sensitive and selective colorimetric detection of DA by using two specific ligands modified Ag nanoparticles, where the DA molecules can make dual recognition with high specificity. The colloidal suspension of modified Ag nanoparticles was agglomerated after interacting with DA, while the color of Ag nanoparticles suspension changed from yellow to brown, arising from the interparticle plasmon coupling during the aggregation of Ag nanoparticles. The modified Ag nanoparticles suspension and agglomeration were con- firmed by transmission electron microscope images. The optical properties behind the color change were thoroughly investi- gated by using UV-Vis and Raman techniques. The changes in pH, zeta potential, particle size and surface charge density by adding DA were also determined by using dynamic light scattering measurements. The detection limits of modified Ag probes for DA was calculated to be 6.13×10 6 mol L-1 （S/N=2.04） and the correlation co-efficient was determined to be 0.9878. Be- cause of the simplicity in operation and instrumentation of the colorimetric method, this work may afford a feasible, fast ap- proach for detecting and monitoring the DA levels in physiological and pathological systems.