EXAFS characterization of confined gold nanoparticles for the detection of small molecules in label-free impedance aptasensors

A. S. PEINETTI; H. CERETTI; M. MIZRAHI; G.A. GONZÁLEZ; S. A. RAMÍREZ; F.G. REQUEJO; J. M. MONTSERRAT; F. BATTAGLINI

Campinas

Congreso; 26th RAU Annual Users Meeting LNLS/CNPEM; 2016

LNLS/CNPEM

Nanotechnology has expanded the applications of previously known molecules, like DNA and RNA oligonucleotides, developing uses as diverse as image guided cancer therapy to nanostructures for biosensing. In this last field, small molecules are an interesting analytical target because their important roles in many fields such as serving as cell signaling molecules, as drugs in medicine, as pesticides in farming, and many others. In this work, a controlled architecture of nanoelectrodes, with a similar size to small molecule-binding aptamers, is synthesized inside nanoporous alumina. Au nanoparticles are electrogenerated in the alumina cavities showing a fast electron transfer process toward ferrrocyanide. These caped-free nanoparticles (Al/Al2O3/AuNP) are easily modified with thiol-containing aptamers (Al/Al2O3/AuNP/X-SDNA) for the label-free detection of adenosine monophosphate (Al/Al2O3/AuNP/X-SDNA-AMP) by electrochemical impedance spectroscopy (EIS). When the AMP is recognized, the aptamer configuration change in this small confined surface dramatically modifies the ability of the probe to access the AuNP. For the sample Al/Al2O3/AuNP/S-APT, a nanoparticle size of 2.2 nm and a sulfur coverage of ca. 60% were estimated by Extended X-Ray Absorption Fine Structure (EXAFS) at Au L3-edge. EIS and EXAFS results show that the use of a small electrical conducting surface inside an insulating environment can be very sensitive to conformational changes, introducing a new approach to the detection of small molecules exemplified here by the direct and selective detection of adenosine monophosphate (AMP) at nanomolar concentrations.