Encoded particles are one of the most powerful approaches for multiplex high-throughput screening. Surface-enhanced Raman scattering (SERS) based codification can, in principle, avoid many of the intrinsic limitations due to conventional alternatives, as it decreases the reading time and particle size while allowing for almost unlimited codification. Unfortunately, methods for the synthetic preparation of these particles are tedious; often subjected to limited reproducibility (associated with large fluctuations in the size distributions of the polymers employed in the standard protocols); and to date, limited to a small amount of molecules. Herein, we report a universal, one-pot, inexpensive, and scalable synthetic protocol for the fabrication of SERS-encoded nanoparticles. This synthetic strategy is highly reproducible, independent of the chemical nature and size of the Raman code used (31 different codes were tested) and scalable in the liter range without affecting the final properties of the encoded structures. Furthermore, the SERS efficiency of the fabricated encoded nanoparticles is superior to that of the materials produced by conventional methods, while showing a remarkable reproducibility from batch to batch. This encoding strategy can easily be applied to nanoparticles of different materials and shapes.

Efficient treatments in bacterial infections require the fast and accurate recognition of pathogens, with concentrations as low as one per milliliter in the case of septicemia. Detecting and quantifying bacteria in such low concentrations is challenging and typically demands cultures of large samples of blood (~1 milliliter) extending over 24–72 hours. This delay seriously compromises the health of patients. Here we demonstrate a fast microorganism optical detection system for the exhaustive identification and quantification of pathogens in volumes of biofluids with clinical relevance (~1 milliliter) in minutes. We drive each type of bacteria to accumulate antibody functionalized SERS-labelled silver nanoparticles. Particle aggregation on the bacteria membranes renders dense arrays of inter-particle gaps in which the Raman signal is exponentially amplified by several orders of magnitude relative to the dispersed particles. This enables a multiplex identification of the microorganisms through the molecule-specific spectral fingerprints.

Staphylococcus aureus is a common cause of serious infections. One of the main drawbacks in its treatment is the time required for a positive diagnosis, over 24 h, as most methods are still based in bacterial culture. Herein, a microfluidic optical device for the rapid and ultrasensitive quantification of S. aureus in real human fluids is designed. In this approach, the surface‐enhanced Raman scattering (SERS)‐encoded particles, functionalized with either an antibody or an aptamer, form a dense collection of electromagnetic hot spots on the surface of S. aureus. This allows for an exponentially increase of the SERS signal when particles accumulate on the microorganism as compared to their free condition in bulk solution. Quantification is achieved by passing the sample through a microfluidic device with a collection window where a laser interrogates and classifies each of the induced bacteria–nanoparticle aggregates in real time. Further, the advantages of using aptamers versus antibodies as biorecognition elements are extensively investigated.

Rapid advances in nanofabrication techniques of reproducibly manufacturing plasmonic substrates with well-defined nanometric scale features and very large electromagnetic enhancements paved the way for the final translation of the analytical potential of surface-enhanced Raman scattering (SERS) to real applications. A vast number of different SERS substrates have been reported in the literature. Among others, discrete particles consisting of an inorganic micrometric or sub-micrometric core homogeneously coated with plasmonic nanoparticles stand out for their ease of fabrication, excellent SERS enhancing properties, long-term optical stability and remarkable experimental flexibility (manipulation, storage etc). In this article, we performed a systematic experimental study of the correlation between the size of quasi-spherical gold and silver nanoparticle and the final optical property of their corresponding assembles onto micrometric polystyrene (PS) beads. The size and composition of nanoparticles play a key role in tuning the SERS efficiency of the hybrid material at a given excitation wavelength. This study provides valuable information for the selection and optimization of the appropriate PS@NPs substrates for the desired applications.

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Biosensors, especially those with a SERS readout, are required for an early and precise healthcare diagnosis. Unreproducible SERS platforms hamper clinical SERS. Here we report a synthetic procedure to obtain stabile, reproducible and robust highly-SERS performing nanocomposites for labelling. We controlled the NPs agglomeration and codification which resulted in an increased number of hot spots, thus exhibiting reproducible and superior Raman enhancement. We studied fundamental aspects affecting the plasmonic thiol bond resulting in pH exhibiting a determining role. We validated their biosensing performance by designing a SERS-based detection assay model for SARS-CoV-2. The limit of detection of our assay detecting the spike RBD was below 10 ng/mL.