Poly(amidoamine)-Dendrimer-Modified Gold Surfaces for Anomalous Reflection of Gold To Detect Biomolecular Interactions

Abstract

Label-free protein detecting chip technology has encouraged a number of discoveries, as it is a powerful analytical tool in the postgenomic era. In particular, we have focused on a unique characteristic of anomalous reflection of gold (AR) as a new class of label-free detection method for a protein chip system. In this paper, in order to improve the sensitivity of detection of biomolecular interactions by the AR method, we have constructed three-dimensional (3D) nanostructures on gold surfaces with a series of well-defined structures of poly(amidoamine) dendrimers (PAMAMs) from generation 2 to 4 (G2, G3, and G4) tethering biotin moieties as capturing agents for avidin and antibiotin IgG. Comparison of features of such 3D nanostructured surfaces with a diamine-modified flat-like surface revealed a 2-fold increase in the amount of avidin for 3D surfaces relative to the flat surface, and surface-assisted nonspecific interactions were significantly suppressed. We thus obtained 91% coverage for avidin detection on the PAMAM G4-modified surface, indicating a theoretically maximum attainable absorption considering a hexagonal-packed arrangement as a saturated monomolecular layer. In the antibiotin IgG assay, the PAMAM G4-modified surface clearly improved the amount of proteins captured compared to that for the flat surface, indicating that an appropriate density of capturing agents played a more important role in the interaction of larger molecular-sized proteins such as antibiotin IgG, which requires more space for interaction than the medium-sized avidin. These findings should assist in the development of a simple and practical tool for high-throughput protein detection, particularly with the AR method.

Bioinert surface to protein adsorption with higher generation of dendrimer SAMs

“…(1) [16,31]. Dendrimer SAMs act like polymer brush, and the densities of the polymer brushes are controlled by the generation of dendrimers [21,22]. We approximately regarded dendrimer SAMs as one of the polymer brush because Eq.…”

“…For example, interfaces with poly(amidoamine) (PAMAM) dendrimer SAM have been prepared with various generations [19,20]. However, there have been few reports regarding protein adsorption on the dendritic polymer brush, except for some reports representing excellent bioinertness for protein adsorption on high generation dendrimer coated surfaces [21,22]. The dendritic polymer brush has a high density of terminal group, which has the advantage of regulating protein adsorption, compared with the linear polymer brush [23,24].…”

Dendrimers

“…167,168 Finally, an optical fibre-based assay for the quantification of anomalous reflection on gold chips where amine-terminated PAMAM dendrimers are coupled to the gold surface has been described. 169,170 A number of automated heterogeneous immunoassays based on dendrimer nanotechnology are commercially available for assaying changes in blood levels of different clinically significant markers related to a variety of pathogenic conditions. For example, the Stratus (Siemens, Erlangen, Germany) assay protocol is used for the analysis of different cardiac markers, and reduced the heart infarction diagnosis time from more than 1 h to a few minutes.…”

Dendrimer‐Based Sensors

“…The anomalous reflection (AR) of the gold surface containing the PAMAM dendrimers tethered with biotin was used for the detection of avidin and antibiotin lgG by Mihara [110]. The dendrimer-based three-dimensional surface was found to capture significantly more of the proteins than the nondendritic flat surface.…”