Gold Nanoparticle Enlargement Coupled with Fluorescence Decrease for Highly Sensitive Detection of Analytes
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Gold Nanoparticle Enlargement Coupled with Fluorescence Decrease for Highly Sensitive Detection of Analytes Seong Yoon Lim, Jae Hong Kim, Joon Seok Lee, and Chan Beum Park* Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology 335 Science Road, Daejeon 305-701, Republic of Korea ABSTRACT We present a versatile and facile route for highly sensitive detection of analytes through coupling the enlargement of gold nanoparticles (Au NPs) with fluorescence decrease. The fluorescence intensity of dye molecules (e.g., fluorescein or rhodamine B) significantly decreased with the increasing concentration of reducing agents, such as hydrogen peroxide and hydroquinone. The sensitivity for the detection of reducing agents was much higher than other detection methods based on the absorbance measurement of enlarged gold nanoparticles or quantum dot-enzyme hybridization. We could successfully detect acetylthiocholine with the detection limit of several nM orders, using an enzymatic reaction by acetylcholinesterase, a key route for the detection of toxic organophosphate compounds. The fluorescence decreasing approach described in this work requires only a simple addition of fluorescence dye to the reaction solution without any chemical modification. The strategy of fluorescence decrease coupled with nanoparticle growth will be applied on the fluorescent substrate to develop detection templates for highly sensitive optical biosensor. INTRODUCTION Recent advances in nanotechnology enable the participation of nanoparticles as a key component in the assay of various biological events. The activities of various redox enzymes were assayed by measuring the absorbance change of Au NPs, which change occurs when Au NPs grow through the reduction of Au ions by reducing agents, such as H2O2, produced during the enzymatic reactions.1 Herein, we report that the sensitivity of analyte detection can be greatly enhanced if the Au NP enlargement is coupled with a quenching of fluorescent dyes. H2O2, Hydroquinone (HQ) and acetylthiocholine were used as target analytes. HQ is a phenolic pollutant that can enter the body and can erode the skin or inhibit the nervous system.2 Acetylthiocholine is a substrate of an enzyme acetylcholine esterase (AChE) which was chosen as a model enzyme, since the measurement of AChE activity is known to be a key route for the detection of toxic organophosphate compounds, such as nerve agents or pesticides, which inhibit AChE.3 The detection of HQ and acetylthiocholine using AChE can be extended in the applications for the environmental monitoring or national security. As sensitivity is a key factor in the design of biosensors, significant effort has been made to develop fluorescence-based optical biosensors due to their high sensitivity.4,5 Au NPs were previously introduced to fluorescence-based assays to detect biologically important analytes,6-8 and the assays rely mostly on fluorescence resonance energy transfer (FRET) phenomena. However, the design of detection probes based
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