Label-Free Surface Enhanced Raman Scattering (SERS) on Centrifugal Silver Plasmonic Paper (CSPP): A Novel Methodology for Unprocessed Biofluids Sampling and Analysis

Label-free SERS is a powerful bio-analytical technique in which molecular fingerprinting is combined with localized surface plasmons (LSPs) on metal surfaces to achieve high sensitivity. Silver and gold colloids are among the most common nanostructured substrates used in SERS, but since protein-rich samples such as serum or plasma can hinder the SERS effect due to protein–substrate interactions, they often require a deproteinization step. Moreover, SERS methods based on metal colloids often suffer from a poor reproducibility. Here, we propose a paper-based SERS sampling method in which unprocessed human serum samples are first soaked on paper strips (0.4 × 2 cm2), and then mixed with colloidal silver nanoparticles by centrifugation to obtain a Centrifugal Silver Plasmonic Paper (CSPP). The CSPP methodology has the potential to become a promising tool in bioanalytical SERS applications: it uses common colloidal substrates but without the need for sample deproteinization, while having a good reproducibility both in terms of overall spectral shape (r > 0.96) and absolute intensity (RSD < 10%). Moreover, this methodology allows SERS analysis more than one month after serum collection on the paper strip, facilitating storage and handling of clinical samples (including shipping from clinical sites to labs).

Rationalization of In-Situ Synthesized Plasmonic Paper for Colorimetric Detection of Glucose in Ocular Fluids

Tear glucose is an intriguing biofluid that includes potential biomarkers. While many sensors have emerged nowadays, there is still demand for advanced sensors with nonenzymatic, simple, cost-effective sensing mechanism. Herein, we present a paper-based colorimetric assay by utilizing a gold nanoparticle formation. Experimental characterization substantiated a mechanism in this in situ reduction. Scanning electron microscopy, UV-visible spectrometry, etc. were involved in the scrutiny. As a result, we reached for the rationale whereas the particle formation can be utilized for a glucose sensing using tears. This paper-based detection was insusceptible to physiological tear matrix, i.e., chloride ion effect, false-positive error and synergistic effect by antioxidants. In addition, we evaluated its analytical performance in an artificial tear assay. Of the obtained a linear regressions, the concentration range corresponded to the physiological or pathologic reference range. In addition, within the low-concentration range, a high correlation was resulted 0.965. Furthermore, we investigated statistical validation by employing the Bland–Altman plot. In the end sections of this paper, we denoted its ready-to-use merits by simplicity—as well as the further application of our plasmonic paper.

Versatile Polypeptide-Functionalized Plasmonic Paper as Synergistic Biocompatible and Antimicrobial Nanoplatform

Nowadays, thanks to nanotechnological progress, which itself guides us more and more closely toward not only the efficient design of innovative nanomaterials or nanostructures, but to the improvement of their functionality, we benefit from an important asset in the battle against pathogenic illnesses. Herein, we report a versatile biocompatible plasmonic nanoplatform based on a Whatman paper incorporating positively-charged gold nanospherical particles via the immersion approach. The morphological characterization of the as-engineered-plasmonic paper was examined by SEM (scanning electron microscopy) and HRTEM (high-resolution transmission electron microscopy) investigations, while its surface chemical modification with a synthetic polypeptide, specifically RRWHRWWRR-NH2 (P2), was proved by monitoring the plasmonic response of loaded gold nanospheres and the emission signal of P2 via fluorescence spectroscopy. The as-functionalized plasmonic paper is non-cytotoxic towards BJ fibroblast human cells at bactericidal concentrations. Finally, the antimicrobial activity of the P2-functionalized plasmonic paper on both planktonic bacteria and biofilms was tested against two reference strains: Gram-positive Bacteria, i.e., Staphylococcus aureus and the Gram-negative Bacteria, i.e., Escherichia coli, determining microbial inhibition of up to 100% for planktonic bacteria. In line with the above presented nanoplatform’s proper design, followed by their functionalization with active antimicrobial peptides, new roads can be open for determining antibiotic-free treatments against different relevant pathogens.