Immunoimaging scanning probe microscopy was utilized for the low-level detection and quantification of biotinylated G4 poly(amidoamine) PAMAM dendrimers. Results were compared to those of high-performance liquid chromatography (HPLC) and found to provide a vastly improved analytical method for the low-level detection of dendrimers, improving the limit of detection by a factor of 1000 ( ？moles). The biorecognition method is reproducible and shows high specificity and good accuracy. In addition, the capture assay platform shows a promising approach to patterning dendrimers for nanotechnology applications. 1. Introduction Dendrimers are at the forefront of research in nanoscience due to the many interesting properties of these macromolecular systems including their precise architecture, highly reproducible shape, high uniformity and purity, low immunogenicity and toxicity, high loading capacity, and high shear resistance [1–5]. They have shown a great deal of versatility with applications in numerous areas such as drug delivery [6, 7], gene therapy [8, 9], chemotherapy [10], electrochemistry [11, 12], metal recovery [13], catalysis [14, 15], and sensors [16–18]. Development of new low-level detection and quantification methods is needed with the utilization of these nanomaterials. Currently, high-performance liquid chromatography (HPLC) is the predominate approach reported for dendrimer quantification [19, 20]. However, the primary focus of HPLC, along with capillary electrophoresis, has been to evaluate dendrimer purity and degree of conjugation [21–27]. Little has been reported within the literature with regard to the advancement of new quantification methods for dendrimers. This work introduces a biorecognition readout technique that has the potential to provide low-level detection of dendrimers. Biotinylated poly(amidoamine) PAMAM dendrimers were chosen as a model target. PAMAM dendrimers, which are highly water soluble, represent the most widely studied class of dendrimers. Functionalization of PAMAM dendrimer surfaces has proven useful in their utilization for various applications including drug delivery and chemical sensing [5, 6, 16]. Biotin-labeled dendrimers have been utilized in tumor [28] and antibody [29] targeting studies and biosensor design [30]. Biotinylated PAMAM dendrimers may also have the potential for delivering therapeutic drugs to the brain [31, 32]. We report here a readout method using an immunoassay platform and scanning probe microscopy (SPM) for low-level quantification of biotinylated G4 PAMAM dendrimers. The assay takes
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