Here, we present new antimicrobial nanoparticles based on silica nanoparticles (SNPs) coated with a quaternary ammonium cationic surfactant, didodecyldimethylammonium bromide (DDAB). Depending on the initial concentration of DDAB, SNPs immobilize between 45 and 275 μg of DDAB per milligram of nanoparticle. For high concentrations of DDAB adsorbed to SNP, a bilayer is formed as confirmed by zeta potential measurements, thermogravimetry, and diffuse reflectance infrared Fourier transform (DRIFT) analyses. Interestingly, these nanoparticles have lower minimal inhibitory concentrations (MIC) against bacteria and fungi than soluble surfactant. The electrostatic interaction of the DDAB with the SNP is strong, since no measurable loss of antimicrobial activity was observed after suspension in aqueous solution for 60 days. We further show that the antimicrobial activity of the nanoparticle does not require the leaching of the surfactant from the surface of the NPs. The SNPs may be immobilized onto surfaces with different chemistry while maintaining their antimicrobial activity, in this case extended to a virucidal activity. The versatility, relative facility in preparation, low cost, and large antimicrobial activity of our platform makes it attractive as a coating for large surfaces.

We assembled a new electrospinning apparatus and used poly(ethylene oxide) as a model polymer to perform a systematic study on the influence of solution and processing parameters on the morphology of electrospun nanofibers. Solution parameters studied were polymer concentration and molecular mass. The solvent used, 60 wt% water, 40 wt% ethanol, was the same throughout the study. Processing parameters analyzed were: solution feed rate, needle tip-collector distance and electrostatic potential difference between the needle and collector. Solution viscosity increased both with polymer concentration and molecular mass. Polymer concentration plays a decisive role on the outcome of the electrospinning process: a low concentration led to the formation of beaded fibers; an intermediate concentration yielded good quality fibers; a high concentration resulted in a bimodal size distribution and at even higher concentration a distributed deposition. Fiber diameter increased with polymer molecular mass and higher molecular masses are associated with a higher frequency of splaying events. Fiber diameter increased linearly with solution feed rate. While an increase in needle-collector distance represents a weaker electric field, a greater distance to be covered by the fibers and a longer flight time, presumably favoring the formation of thinner fibers, as solvent evaporation leads to a local increase of concentration and viscosity, viscoelastic forces opposing stretching caused an increase of fiber diameter with needle-collector distance. A higher voltage applied at the needle is associated with a higher charging of the polymer and a higher electrical current through it ultimately leading to incomplete solvent evaporation and merged fibers being produced. Controlling the charging of the polymer independently of the electric field strength was achieved by applying a voltage to the collector while distance and potential difference were kept constant. The increased electrostatic repulsion associated with an increase of the high voltage applied to the needle led to the disappearance of merged fibers.

Porphyrins are typically weak emitters, which presents challenges to their optical detection by single-molecule fluorescence microscopy. In this contribution, we explore the enhancement effect of gold nanodimer antennas on the fluorescence of porphyrins in order to enable their single-molecule optical detection. Four meso-substituted free-base porphyrins were evaluated: two cationic, one neutral, and one anionic porphyrin. The gold nanodimer antennas are able to enhance the emission from these porphyrins by a factor of 105–106 increase in the maximum detected photon rates. This extreme enhancement is due to the combination of an antenna effect on the excitation rate that is estimated to be above 104-fold and an emission efficiency that corresponds to an increase of 2–10 times in the porphyrin’s fluorescence quantum yield.

Proteases play a pivotal role in several biological processes, from digestion, cell proliferation, and differentiation to fertility. Deregulation of protease metabolism can result in several pathological conditions (i.e., cancer, neurodegenerative disorders, and others). Therefore, monitoring proteolytic activity in real time could have a fundamental role in the early diagnosis of these diseases. Herein, the main approaches used to develop biosensors for monitoring proteolytic activity are reviewed. A comparison of the advantages and disadvantages of each approach is provided along with a discussion of their importance and promising opportunities for the early diagnosis of severe diseases. This new era of biosensors can be characterized by the ability to control and monitor biological processes, ultimately improving the potential of personalized medicine. Biosensing in Personalized Medicine: The Emergence of Protease BiomarkersA deep understanding of the individual characteristics of biological processes and precise control of responses and feedback to therapies are essential in a world that is running towards personalized medicine (see Glossary). Recent reports predict that this market will grow at a compound annual growth rate (CAGR) of over 11% from US$92.4 billion dollars in 2017 to US$194.4 billion in 2024 (https://www.researchandmarkets.com/research/n5kqz7/global?w=5), with oncology responsible for 30% of the revenues generated. Biosensors are one of the underlying technologies of personalized medicine, giving support to the highly informed decisions that are critical to obtain better clinical outcomes and to decrease undesired side-effects. Compared with the personalized medicine market, a similar tendency is observed for the biosensors market where growth from US$18.6 billion dollars in 2018 to US$31.5 billion in 2025 (8% CAGR) is expected (https://www.gminsights.com/industry-analysis/biosensors-market).One of the primary goals of a biosensor is to determine the presence/absence or activity of a given biomarker and to correlate these results with pathophysiological conditions. Proteases are emerging as a new category among the wide variety of biomarkers targeted by biosensors due to their key role in health and disease. In this review, we present the main approaches used to measure proteolytic activity in real timefor both in vivo and in vitro applicationsand discuss recent developments in and future possibilities for protease biosensors (Figure 1A). The Roles and Idiosyncrasies of Proteases: Why Monitor Proteolytic Activity?Proteases are a widely explored research topic as illustrated by more than 487 000 entries registered in PUBMED. However, it was only recently that proteases emerged as an analyte of interest for biosensing [68]. These hydrolytic enzymes (EC 3.4) play a pivotal role in several biological processes, such as digestion, cell proliferation, and differentiation [1], as well as apoptosis [2], coagulation [3], immunity [4], and fertility [5]. The deregulation of protease metabolism can resul...