A 3D plasmonic sensing platform that combines the properties of citrate gold nanoparticles (AuNPs) and poly-(ethylene glycol) diacrylate (PEGDA) hydrogels is proposed as a nanocomposite hybrid material for biosensing applications, whose optical properties and sensitivity can be tuned by varying the particle mean diameter as also predicted by the Mie theory. It is found that AuNPs embedded in the hydrogel network are more stable when compared to the colloidal aqueous solutions. PEGDA hydrogel physically retains the gold nanoparticles even after a full swelling process during immersion in liquids. Such a property is confirmed by exposing the AuNPs-containing PEGDA hydrogels to organic solvents and buffers that would usually cause the aggregation of the nanoparticles in solution. Moreover, biotin, as a small molecule model, has been captured, and optically detected with a transmission mode customized setup, by a cysteamine modified AuNPs-containing PEGDA hydrogel layer to achieve a biorecognition hybrid device.
This review summarizes the leading advancements in porous silicon (PSi) optical-biosensors, achieved over the past five years. The cost-effective fabrication process, the high internal surface area, the tunable pore size, and the photonic properties made the PSi an appealing transducing substrate for biosensing purposes, with applications in different research fields. Different optical PSi biosensors are reviewed and classified into four classes, based on the different biorecognition elements immobilized on the surface of the transducing material. The PL signal modulation and the effective refractive index changes of the porous matrix are the main optical transduction mechanisms discussed herein. The approaches that are commonly employed to chemically stabilize and functionalize the PSi surface are described.
Food packaging is not only a simple protective barrier, but a real “active” component, which is expected to preserve food quality, safety and shelf-life. Therefore, the materials used for packaging production should show peculiar features and properties. Specifically, antimicrobial packaging has recently gained great attention with respect to both social and economic impacts. In this paper, the results obtained by using a polymer material functionalized by a small synthetic peptide as “active” packaging are reported. The surface of Polyethylene Terephthalate (PET), one of the most commonly used plastic materials in food packaging, was plasma-activated and covalently bio-conjugated to a bactenecin-derivative peptide named 1018K6, previously characterized in terms of antimicrobial and antibiofilm activities. The immobilization of the peptide occurred at a high yield and no release was observed under different environmental conditions. Moreover, preliminary data clearly demonstrated that the “active” packaging was able to significantly reduce the total bacterial count together with yeast and mold spoilage in food-dairy products. Finally, the functionalized-PET polymer showed stronger efficiency in inhibiting biofilm growth, using a Listeria monocytogenes strain isolated from food products. The use of these “active” materials would greatly decrease the risk of pathogen development and increase the shelf-life in the food industry, showing a real potential against a panel of microorganisms upon exposure to fresh and stored products, high chemical stability and re-use possibility.
Aptamers are artificial nucleic acid ligands identified and obtained from combinatorial libraries of synthetic nucleic acids through the in vitro process SELEX (systematic evolution of ligands by exponential enrichment). Aptamers are able to bind an ample range of non-nucleic acid targets with great specificity and affinity. Devices based on aptamers as bio-recognition elements open up a new generation of biosensors called aptasensors. This review focuses on some recent achievements in the design of advanced label-free optical aptasensors using porous silicon (PSi) as a transducer surface for the detection of pathogenic microorganisms and diagnostic molecules with high sensitivity, reliability and low limit of detection (LoD).
Fresh products are characterized by reduced shelf-life because they are an excellent growth medium for a lot of microorganisms. Therefore, the microbial spoilage causing significant food supply losses has become an enormous economic and ethical problem worldwide. The antimicrobial packaging is offering a viable solution to tackle this economic and safety issue by extending the shelf-life and improving the quality and safety of fresh products. The goal of this study was to investigate the effects of a food contact surface of polyethylene terephthalate (PET) functionalized with the previously characterized antimicrobial peptide mitochondrial-targeted peptide 1 (MTP1), in reducing the microbial population related to spoilage and in providing the shelflife stability of different types of fresh foods such as ricotta cheese and buffalo meat. Modified polymers were characterized concerning the procedure of plasma-activation by water contact angle measurements and Fourier transform infrared spectroscopy measurements in attenuated total reflection mode (ATR-FTIR). Results showed that the MTP1-PETs provided a strong antimicrobial effect for spoilage microorganisms with no cytotoxicity on a human colon cancer cell line. Finally, the activated polymers revealed high storage stability and good reusability. This study provided valuable information to develop alternative antimicrobial packaging for enhancing and extending the microbial quality and safety of perishable foods during storage.
more complex systems, such as microelectronics and microfluidics, without compromising high sensitivity and mass production. [5] Among the many available polymeric materials, hydrogels represent the ideal substrates for plasmonic sensors due to their optical transparency, biocompatibility, and their swelling capability in presence of an aqueous environment. [6][7][8] Hydrogels are generally recognized as 3D architectures, whose crosslinking density, mesh network size, and polymerization agent can be tuned and selected according to the desired applications. Moreover, they can be easily engineered and made responsive to external stimuli, [9] this being crucial when designing analytical platforms with applications in biochemical sensing. [8,10] In this context, when properly assembled and functionalized, noble metal nanoparticles (NPs), basically silver (Ag), and gold (Au), represent the ideal transducers since they can show a dramatically high response upon exposure to a target analyte. In some cases, the transduction is visible to the naked eye, especially in liquid colorimetric assays, which exploit the capability of plasmonic nanoparticles to aggregate, undergoing deep color variations. [11][12][13] Even if very effective and similar to the Enzyme-Linked Immunosorbent Assay (ELISA) commercial kits, the liquid phase plasmonic assays could suffer from pH, ionic strength, and temperature both during the preparation of the assay and the measurement procedure itself. [14][15][16] To overcome these limitations without giving up the sensing advantages provided by plasmonic nanoparticles, both top-down and bottom-up fabrication strategies have been proposed to arrange them in periodic, quasiperiodic, and random arrays on different substrates. [17][18][19] Different transduction mechanisms have been proposed to design plasmonic biochemical sensors and to ensure high sensitivity and specificity. However, portability and ease of use of these optical devices still represent a hard-to-solve challenge. All these transduction mechanisms are based on the localized surface plasmon resonance (LSPR) exhibited by noble-metal NPs. [20,21] Refractometric biosensors exploit the LSPR shifts as a function of a target analyte when properly interacting with the biorecognition element adhered on the surface of the NPs; [22,23] Surface-enhanced infrared absorption (SEIRA) and surface-enhanced raman scattering (SERS) exploit the LSPR to enhance infrared and Raman signals of molecules onto plasmonic substrates; [24][25][26] Metal-enhanced fluorescence (MEF), also referred to as plasmon-enhanced fluorescence A hybrid plasmonic transducer made of a Poly-(ethylene glycol) diacrylate (PEGDA) hydrogel and citrate gold nanoparticles detects the biotin-streptavidin interaction at picomolar (× 10 −12 m ) concentrations. The all-solution fabrication strategy, herein proposed, is large-scale, easily tunable, and low-cost; nevertheless, this innovative device is highly reproducible and optically stable, and it can be used in dual-optical mode. Indeed, b...
Graphene oxide (GO) is a two-dimensional material with peculiar photoluminescence emission and good dispersion in water, that make it an useful platform for the development of label-free optical biosensors. In this study, a GO-porous silicon (PSi) hybrid device is realized using a covalent chemical approach in order to obtain a stable support for biosensing applications. Protein A, used as bioprobe for biosensing purposes, is covalently linked to the GO, using the functional groups on its surface, by carbodiimide chemistry. Protein A bioconjugation to GO-PSi hybrid device is investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), water contact angle (WCA) measurements, Fourier transform infrared (FTIR) spectroscopy, steady-state photoluminescence (PL), and fluorescence confocal microscopy. PSi reflectance and GO photoluminescence changes can thus be simultaneously exploited for monitoring biomolecule interactions as in a multi-parametric hybrid biosensing device.
Plasmonic Transducers In article number 2101425, Bruno Miranda, Carlo Forestiere, and co‐workers report on hydrogel‐based, high‐sensitivity, hybrid plasmonic transducers for monitoring biomolecular interactions. The hydrogel network physically stabilizes gold nanoparticles, which act as biochemical optical transducers both in spectroscopy and fluorescence.
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