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    Quantifying Analyte Surface Densities and Their Distribution with Respect to Electromagnetic Hot Spots in Plasmon-Enhanced Spectroscopic Biosensors

    Year: 2021

    Journal: J. Phys. Chem. C, Volume 125, MAY 13, page 9866–9874

    Authors: Rastogi, Rishabh; Beggiato, Matteo; Foli, Ekoue A. Dogbe; Vincent, Remi; Dupont-Gillain, Christine; Adam, Pierre-Michel; Krishnamoorthy, Sivashankar

    Organizations: National Research Funding Agency of Luxembourg (FNR) via project PLASENS [C15/MS/10459961]; National Research Funding Agency of Luxembourg (FNR) via project VIRANOSTIC; National Research Funding Agency of Luxembourg (FNR) via project MASSENA; INTERREG Grand Region V (IMPROVESTEM); EU COST Action BIONECA; Fonds europeen de developpement economique et regional (FEDER)

    Nanoplasmonic sensors based on surface-enhanced spectroscopies carry profound promise toward ultrasensitive detection of biomolecular analytes within miniaturized measurement footprints. High sensitivity in these sensors is achieved by intense electromagnetic (EM) enhancements at hot spots and colocalization of analytes with such hot spots. However, EM hot spots exhibiting high EM enhancements often present confined areas that render them inaccessible to large analytes such as biomolecules. Addressing this requires rational engineering of a nanoplasmonic interface that factors in the analyte surface concentrations and how they are distributed with respect to the EM hot spots. Here we demonstrate combination of metal-enhanced fluorescence (MEF) with a quartz crystal microbalance (QCM) through fabrication of highly resolved plasmonic nanoarrays directly on the QCM sensor. QCM and MEF are simultaneously employed to monitor in situ, real-time binding of fluorescently labeled protein to receptor-functionalized plasmonic arrays. The correlation between the QCM and MEF responses is used to quantify surface density of protein that contributes to the MEF signal intensities and obtain analyte distribution with respect to the EM hot spots by geometric modeling. Results further reveal the MEF assays to be sensitive down to similar to 2 zmol of protein within measurement footprints that are 8 orders of magnitude smaller than that of the QCM.
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