Nanoparticle Imprinted Polymers As Sensing Layers for Size-Selective Recognition of Silver Nanoparticles

Abstract

The expected broad utilisation of nanoparticles (NPs) calls for a detailed consideration of their specific toxicological effects and monitoring their release into the environment (nanotoxicology).[1] Appropriate in vitro sensing tools should provide information about the possible interaction between nanoobjects (characterized by core material, size, shell chemistry and shape) and biological systems. Recently, we published a new concept based on nanoparticle-imprinted polymers (NIPs, Figure 1) combined with electrochemical detection.[2] The new sensor principle was first demonstrated with a polyaniline film transferred simultaneously with template AuNPs by the Langmuir-Blodgett technique. Here we demonstrate the extension of this concept to other matrix systems and other strategies for building NIPs. AuNPs with a diameter of 30 nm were arranged as templates on a 3-aminopropyltriethoxysilan (APTES)-modified indium tin oxide (ITO) electrode. Electrostatic interactions between negatively charged AuNPs and the positively charged monolayer enabled a controlled assembly of dispersed NPs as evidenced by scanning electron microscopy (SEM) and scanning force microscopy (SFM). Subsequently, a polymer matrix is generated either by electropolymerisation of self-inhibiting poly(phenol) and poly(plumbagin) films or by spin-coating an ultrathin poly(dimethylsiloxane) (PDMS) layer. SFM images proved the presence of templates within smooth, 5 to 20 nm thick matrices. Template NPs were chemically removed in potassium cyanide, leaving their shape and size imprinted in the polymer as evidenced by different techniques like SEM and Pulsed Force Microscopy (PFM). The recognition ability and size selectivity of NIPs was investigated by immersing the matrix in aqueous solutions containing citrate-capped AgNPs overnight. The presence of analyte AgNPs was verified electrochemically in an aqueous NaNO3 solution as by LSV. Complementing studies by UV-Vis and X-ray photoelectron spectroscopies corroborated the template embedding, template release and analyte NP uptake.