A comparison of mono and multivalent linkers and their effect on the colloidal stability of nanoparticle and immunoassays performance

When designing devices for biomedical diagnostics, increasing the signal to noise ratio is often critical for achieving clinically relevant sensitivity and limits of detection (LOD). In antibody-based assays, the measured signal can be amplified through the replacement of molecular fluorophores with doped nanoparticles (NP). However, the benefits of using NPs can only be realized if the NPs are coated efficiently with detection antibody, have good colloidal stability and the ratio of specific to non-specific binding (NSB) is high enough. The main focus of this paper is on the optimization of the bioconjugation protocol for antibody labeling of NPs leading to improved assay performance. Two types of linkers were used: monovalent linkers (glutaraldehyde; sulfo-SMCC; and sulfo-SIAB), and three generations of dendrimers endowed with multivalent carboxylic functionality. Overall, the NP-IgG conjugates prepared using multivalent linkers showed a significantly lower LOD and higher sensitivity than their homo- or hetero-functional counterparts. The multivalent dendrimers also improved NP stability and reduced aggregation. Moreover, the dendrimers showed a higher reactivity with biological material, a feature that could significantly reduce the cost of high-throughput biodiagnostics tests.