Label-Free Pb(II) Whispering Gallery Mode Sensing Using Self-Assembled Glutathione-Modified Gold Nanoparticles on an Optical Microcavity

An ultrasensitive assay for the detection of (WGM) sensing. In this technique a photonic microcavity was Pb(II) has been developed using whispering gallery mode aminosilane to promote adhesion of the GSH-modified NPs (Au NPs). The resonator was functionalized using an decorated with glutathione (GSH)-modified gold nanoparticles creating a highly sensitive sensor specific to Pb(II). Upon introduction of Pb(II) solutions via a fluidic cell, Pb(II) ions bind to the GSH-Au NP complex and induce a shift of the resonant wavelength. Using this detection strategy we show that we are able to detect Pb(II) concentrations down to 0.05 nM in the presence of alkaline and heavy metal interferences such as Mg(II), Mn(II), Ca(II), Ni(II), Cd(II), Cr(II), Fe(II), and Hg(II). The signal was found to be proportional to the. Pb(II) concentration within the range of 2.40-48.26 nM and was found to have an association constant of 2.15 X 10(5) M-1 s(-1). The sensitivity obtained shows unparalleled advantages over currently available technology and satisfies the exposure thresholds set out by world organizations such as International Agency for Research on Cancer (IARC) and the Environmental Protection Agency (EPA). We believe that this sensor has the potential to be made portable for applications in environmental monitoring and in-field applications.