Abstract

In this work, we design new plasmonic paper-based nanoplatforms with interesting capabilities in terms of sensitivity, efficiency, and reproducibility for promoting multimodal biodetection via Localized Surface Plasmon Resonance (LSPR), Surface Enhanced Raman Spectroscopy (SERS), and Metal Enhanced Fluorescence (MEF). To succeed, we exploit the unique optical properties of gold nanobipyramids (AuBPs) deposited onto the cellulose fibers via plasmonic calligraphy using a commercial pen. The first step of the biosensing protocol was to precisely graft the previously chemically-formed p-aminothiophenol@Biotin system, as active recognition element for target streptavidin detection, onto the plasmonic nanoplatform. The specific capture of the target protein was successfully demonstrated using three complementary sensing techniques. As a result, while the LSPR based sensing capabilities of the nanoplatform were proved by successive 13–18 nm red shifts of the longitudinal LSPR associated with the change of the surface RI after each step. By employing the ultrasensitive SERS technique, we were able to indirectly confirm the molecular identification of the biotin-streptavidin interaction due to the protein fingerprint bands assigned to amide I, amide III, and Trp vibrations. Additionally, the formed biotin-streptavidin complex acted as a spacer to ensure an optimal distance between the AuBP surface and the Alexa 680 fluorophore for achieving a 2-fold fluorescence emission enhancement of streptavidin@Alexa 680 on the biotinylated nanoplatform compared to the same complex on bare paper (near the plasmonic lines), implementing thus a novel MEF sensing nanoplatform. Finally, by integrating multiple LSPR, SERS, and MEF nanosensors with multiplex capability into a single flexible and portable plasmonic nanoplatform, we could overcome important limits in the field of portable point-of-care diagnostics.

Highlights

  • The design of innovative biosensing devices proving portability, high efficiency, and sensitivity, ease of use and low-cost increases continuously the research interest focused on the development of bio-nanotechnologies for specific diagnostic applications (Jiang et al, 2017)

  • The assessed sizes were than compared with the obtained Dynamic Light Scattering (DLS) results, the hydrodynamic diameter data being in good agreement with the size analysis from the Transmission Electron Microscope (TEM) investigation

  • We developed a new flexible and tunable paperbased nanoplatform having different active plasmonic lines with modulated Localized Surface Plasmon Resonance (LSPR) responses designed by a simple and inexpensive plasmonic calligraphy approach using a commercial pen filled with AuBPs as colloidal inks

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Summary

Introduction

The design of innovative biosensing devices proving portability, high efficiency, and sensitivity, ease of use and low-cost increases continuously the research interest focused on the development of bio-nanotechnologies for specific diagnostic applications (Jiang et al, 2017). Such MEF point-of-care devices were demonstrated to be effective for lowering the detection limit of common detection assays such as immunofluorescence assay (Nooney et al, 2010; Liu et al, 2018) or for the successful ultralow detection of cancer biomarkers (Park et al, 2018; Della Ventura et al, 2019) In this optical process, where fluorophores should be placed near the metal surface at a certain distance to generate fluorescence emission amplification (Pompa et al, 2006; Deng and Goldys, 2012), AuBPs can act as intriguing MEF nanoantennas through giving arise at their two sharp tips to a significantly enhanced local field, which can be further amplified due to the promising structure of the paper by allowing the formation of the intrinsic plasmonic hotspots. Innovative plasmonic paper-based nanoplatforms with highly controllable broad-range tunability of the LSPR response, especially in the NIR biological windows, enabling a confident enhanced multimodal plasmonic SERS and MEF detection of specific antigen-antibody recognition interactions are still lacking from the literature

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