Abstract
Resonance enhanced absorption (REA) nanocolor microfluidic devices are new promising bioassay platforms, which employ nanoparticle‐ (NP‐) protein conjugates for the immunodetection of medically relevant markers in biologic samples such as blood, urine, and saliva. The core component of a REA test device is a PET chip coated with aluminum and SiO2 thin layers, onto which biorecognitive molecules are immobilized. Upon addition of a sample containing the analyte of interest, a NP‐protein‐analyte complex is formed in the test device that is captured on the REA chip, for example, via streptavidin‐biotin interaction. Thereby, a colored symbol is generated, which allows optical readout. Silver enhancement of the bound nanoparticles may be used to increase the sensitivity of the assay. Herein, we demonstrate that adsorptive immobilization via a cationic polymeric interlayer is a competitive and fast technique for the binding of the capture protein streptavidin onto planar SiO2 surfaces such as REA biochips. Moreover, we report the development of a silver enhancement technology that operates even in the presence of high chloride concentrations as may be encountered in biologic samples. The silver enhancement reagents may be integrated into the microfluidic assay platform to be released upon sample addition. Hereby, a highly sensitive one‐step assay can be realized.
Highlights
Modern point-of-care diagnostics strongly relies on low-cost, portable, easy-to-handle platforms especially in regions with limited resources and medical infrastructure.Microfluidic devices called μTAS or lab-on-a-chip systems belong to the most promising technologies studied in this context
The core component of a Resonance enhanced absorption (REA) test device is a PET chip coated with aluminum and SiO2 thin layers, onto which biorecognitive molecules are immobilized
Upon addition of a sample containing the analyte of interest, a NP-protein-analyte complex is formed in the test device that is captured on the REA chip, for example, via streptavidin-biotin interaction
Summary
Modern point-of-care diagnostics strongly relies on low-cost, portable, easy-to-handle platforms especially in regions with limited resources and medical infrastructure. Microfluidic devices called μTAS (micro total analysis systems) or lab-on-a-chip systems belong to the most promising technologies studied in this context. A major part of the respective research focuses on the combination of microfluidics with immunoassay technology being the most valuable tool for the detection of medically relevant markers. Compared to conventional immunoassays microfluidic systems offer efficient mass transport and a reduced surface to volume ratio. Detection strategies currently studied and employed for microfluidic platforms range from fluorimetric over colorimetric to electrochemical techniques (see, e.g., [2]). Where quantification is an issue and low detection limits are most critical, electrochemical systems are generally the first choice. For quick tests and screenings, a noninstrumental readout may be preferred, which implicates a colorimetric detection strategy
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