Facile fabrication of distance-tunable Au-nanorod chips for single-nanoparticle plasmonic biosensors

In this work, we present a simple and effective method to fabricate distance-controllable, Au nanorod (AuNR) chips thorough electrostatic assembly. Cetyltrimethylammonium bromide (CTAB)-capped AuNRs were immobilized on a hydroxyl-functionalized glass substrate by immersion of the glass into AuNR-suspension. The electrostatic surfacial assembly of AuNRs offers significant advantages over conventional thiol-induced chemistry, i.e., direct control of self-assembly of AuNRs, easy fabrication in ambient environment and most importantly, broad range of tunable inter-particle distance, ranging from 0.25 to 10 mu m. The mechanism of time-dependant deposition process of AuNRs was described via competitive bindings of AuNRs and free CTAB molecules in AuNR-suspension. In addition, the electrostatically anchored AuNRs on a glass substrate provide sufficient stability under harsh experimental conditions with flow of basic/acidic solutions and organic solvents with different polarity. The feasibility of the AuNR-chips fabricated by the proposed method for single-nanoparticle plasmonic biosensors was demonstrated by the plasmonic measurement of aptamer-thrombin binding event. The corresponding limit of detection of thrombin molecule was found to be similar to 278 pM based on the signal to noise ratio of 4. (C) 2010 Elsevier B.V. All rights reserved.