Porous Silicon Optical Devices: Recent Advances in Biosensing Applications.

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.

Functionalized Polymeric Materials with Bio-Derived Antimicrobial Peptides for "Active" Packaging.

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.

Porous Silicon-Based Aptasensors: The Next Generation of Label-Free Devices for Health Monitoring.

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).

A structural peculiarity of Antarctic fish IgM drives the generation of an engineered mAb by CRISPR/Cas9.

IgM is the major circulating Ig isotype in teleost fish, showing in Antarctic fish unique features such as an extraordinary long hinge region, which plays a crucial role in antibody structure and function. In this work, we describe the replacement of the hinge region of a murine monoclonal antibody (mAb) with the peculiar hinge from Antarctic fish IgM. We use the CRISPR/Cas9 system as a powerful tool for generating the engineered mAb. Then, we assessed its functionality by using an innovative plasmonic substrate based on bimetallic nanoislands (AgAuNIs). The affinity constant of the modified mAb was 2.5-fold higher than that obtained from wild-type mAb against the specific antigen. Here, we show the suitability of the CRISPR/Cas9 method for modifying a precise region in immunoglobulin gene loci. The overall results could open a frontier in further structural modifications of mAbs for biomedical and diagnostic purposes.

Bioconjugation of Peptides to Hybrid Gold Nanoparticles.

Gold nanoparticles (AuNPs) can be produced by well-assessed synthesis methods and can show a high surface area-to-volume ratio, chemical inertness, high electron density, strong optical absorption as well as low toxicity. AuNPs have been conjugated with many different biomolecules for a wide range of biomedical applications. These applications require an increasingly complex level of surface decoration in order to achieve stability, efficacy, and specific functionalities. This chapter provides detailed instructions about the synthesis of AuNPs and bioconjugation strategies in order to obtain stable hybrid nanomaterials. The described biofunctionalization procedures are based on carbodiimide chemistry and ligand-exchange methods allowing the conjugation of Lys-peptide or Cys-peptide, respectively, to the AuNPs surface.

PNA-Based Graphene Oxide/Porous Silicon Hybrid Biosensor: Towards a Label-Free Optical Assay for Brugada Syndrome.

Peptide nucleic acid (PNA) is a synthetic DNA mimic that outperforms the properties of traditional oligonucleotides (ONs). On account of its outstanding features, such as remarkable binding affinity towards complementary DNA or RNA as well as high thermal and chemical stability, PNA has been proposed as a valuable alternative to the ON probe in gene-sensor design. In this study, a hybrid transducer made-up of graphene oxide (GO) nano-sheets covalently grafted onto a porous silicon (PSi) matrix has been investigated for the early detection of a genetic cardiac disorder, the Brugada syndrome (BS). A functionalization strategy towards the realization of a potential PNA-based device is described. A PNA, able to detect the SCN5A gene associated with the BS, has been properly synthesized and used as a bioprobe for the realization of a proof-of-concept label-free optical PNA-biosensor. PSi reflectance and GO photoluminescence signals were simultaneously exploited for the monitoring of the device functionalization and response.

Time-gated luminescence imaging of positively charged poly-l-lysine-coated highly microporous silicon nanoparticles in living Hydra polyp.

The development of non-toxic fluorescent agents alternative to heavy metal-based semiconductor quantum dots represents a relevant topic in biomedical research and in particular in the bioimaging field. Herein, highly luminescent Si─H terminal microporous silicon nanoparticles with µs-lived photoemission are chemically modified with a two step process and successfully used as label-free probes for in vivo time-gated luminescence imaging. In this context, Hydra vulgaris is used as model organism for in vivo study and validity assessment. The application of time gating allows to pursue an effective sorting of the signals, getting rid of the most common sources of noise that are fast-decay tissue autofluorescence and excitation scattering within the tissue. Indeed, an enhancement by a factor ~ 20 in the image signal-to-noise ratio can be estimated.

Design and Synthesis of Hybrid PEGylated Metal Monopicolinate Cyclam Ligands for Biomedical Applications.

In this study, we report, for the first time, the synthesis of two original nanosystems, based on gold Au(III) and copper Cu(II): simple gold-copper nanoparticles (Cu0AuNPs) and enriched monopicolinate cyclam (L1)-Cu(II)-Au(III)-complex (L1@Cu2+AuNPs). The two nanomaterials differ substantially by the chelation or not of the Cu(II) ions during the NPs synthesis process. The two hybrid nanoparticles (Cu0AuNPs; L1@Cu2+AuNPs) were deeply studied from the chemical and physical point of view, using many different analytical techniques such as Raman and UV-vis spectroscopy, electron transmission microscopy, and dynamic light scattering. Both nanosystems show morphological and good chemical stability at pH 4 values and in physiological conditions during 98 h. Undifferentiated and neural differentiated murine embryonic stem cells were used as a model system for in vitro experiments to reveal the effects of NPs on these cells. The comparative study between Cu0AuNPs and L1@Cu2+AuNPs highlights that copper chelated in its +2 oxidation state in the NPs is more functional for biological application.

Extending the Shelf-Life of Meat and Dairy Products via PET-Modified Packaging Activated With the Antimicrobial Peptide MTP1.

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 shelf-life 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.

Toward Multi-Parametric Porous Silicon Transducers Based on Covalent Grafting of Graphene Oxide for Biosensing Applications.

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.