Electrical monitoring of infection biomarkers in chronic wounds using nanochannels.

Chronic wounds represent an important healthcare challenge in developed countries, being wound infection a serious complication with significant impact on patients' life conditions. However, there is a lack of methods allowing an early diagnosis of infection and a right decision making for a correct treatment. In this context, we propose a novel methodology for the electrical monitoring of infection biomarkers in chronic wound exudates, using nanoporous alumina membranes. Lysozyme, an enzyme produced by the human immune system indicating wound infection, is selected as a model compound to prove the concept. Peptidoglycan, a component of the bacterial layer and the native substrate of lysozyme, is immobilized on the inner walls of the nanochannels, blocking them both sterically and electrostatically. The steric blocking is dependent on the pore size (20-100 nm) and the peptidoglycan concentration, whereas the electrostatic blocking depends on the pH. The proposed analytical method is based on the electrical monitoring of the steric/electrostatic nanochannels unblocking upon the specific degradation of peptidoglycan by lysozyme, allowing to detect the infection biomarker at 280 ng/mL levels, which are below those expected in wounds. The low protein adsorption rate and thus outstanding filtering properties of the nanoporous alumina membranes allowed us to discriminate wound exudates from patients with both sterile and infected ulcers without any sample pre-treatment usually indispensable in most diagnostic devices for analysis of physiological fluids. Although size and charge effects in nanochannels have been previously approached for biosensing purposes, as far as we know, the use of nanoporous membranes for monitoring enzymatic cleavage processes, leading to analytical systems for the specific detection of the enzymes has not been deeply explored so far. Compared with previously reported methods, our methodology presents the advantages of no need of neither bioreceptors (antibodies or aptamers) nor competitive assays, low matrix effects and quantitative and rapid analysis at the point-of-care, being also of potential application for the determination of other protease biomarkers.

Bifunctional Au@Pt/Au core@shell Nanoparticles As Novel Electrocatalytic Tags in Immunosensing: Application for Alzheimer's Disease Biomarker Detection.

In this work, bifunctional core@shell Au@Pt/Au NPs are presented as novel tags for electrochemical immunosensing. Au@Pt/Au NPs were synthesized following a chemical route based on successive metal depositions and galvanic replacement reactions from the starting AuNPs. Au protuberances growth on the surface of Au@Pt NPs allowed their easy bioconjugation with antibodies, while the high catalytic Pt surface area was approached for their sensitive detection through the electrocatalyzed water oxidation reaction (WOR) at neutral pH. Moreover, the synergy between Au and Pt metals on the NP surface also lead to an increased catalytic activity, improving the sensitivity of the NP detection. Cyclic voltammetry and chronoamperometry were used for the evaluation of the Au@Pt/Au NPs electrocatalytic activity toward WOR. The chronoamperometric current recorded at a fixed potential of +1.35 V was selected as the analytical signal, allowing the quantification of Au@Pt/Au NPs at 1013 NPs/mL levels. The optimized electrocatalytic method was applied to the quantification of conformationally altered p53 peptide Alzheimer's disease (AD) biomarker in a competitive immunoassay using magnetic bead (MB) platforms at levels as low as 66 nM. The performance of the system in a real scenario was demonstrated analyzing plasma samples from a cognitively healthy subject. This novel Au@Pt/Au NPs-based electrocatalytic immunoassay has the advantage, over common methods for NP tags electrochemical detection, of the signal generation in the same neutral medium where the immunoassay takes place (0.1 M PBS pH 7.2), avoiding the use of additional and more hazardous reagents and paving the way to future integrated biosensing systems.

Electrochemical quantification of Ag2S quantum dots: evaluation of different surface coating ligands for bacteria determination.

In this work, novel silver sulphide quantum dots (Ag2S QD) are electrochemically quantified for the first time. The method is based on the electrochemical reduction of Ag+ to Ag0 at -0.3 V on screen-printed carbon electrodes (SPCEs), followed by anodic stripping voltammetric oxidation that gives a peak of currents at +0.06 V which represents the analytical signal. The optimized methodology allows the quantification of water-stabilized Ag2S QD in the range of approximately 2 × 109-2 × 1012 QD·mL-1 with a good reproducibility (RSD: 5%). Moreover, as proof-of-concept of relevant biosensing application, Ag2S QD are evaluated as tags for Escherichia coli (E. coli) bacteria determination. Bacteria tagged with QD are separated by centrifugation from the sample solution and placed on the SPCE surface for quantitative analysis. The effect of two different Ag2S QD surface coating/stabilizing agents on both the voltammetric response and the bacteria sensing is also evaluated. 3-mercaptopropionic acid (3-MPA) is studied as model of short length coating ligand with no affinity for the bacteria, while boronic acid (BA) is evaluated as longer length ligand with chemical affinity for the polysaccharides present in the peptidoglycan layer on the bacteria cells surface. The biosensing system allows to detect bacteria in the range 10-1-103 bacteria·mL-1 with a limit of detection as low as 1 bacteria·mL-1. This methodology is a promising proof-of-concept alternative to traditional laboratory-based tests, with good sensitivity and short time and low cost of analysis. Graphical abstractNovel silver sulphide quantum dots (Ag2S QD) are electrochemically quantified for the first time. Moreover, Ag2S QD are evaluated as tags for Escherichia coli bacteria determination. The effect of two different QD surface coating ligands is also evaluated.

Nanoparticles as Emerging Labels in Electrochemical Immunosensors.

This review shows recent trends in the use of nanoparticles as labels for electrochemical immunosensing applications. Some general considerations on the principles of both the direct detection based on redox properties and indirect detection through electrocatalytic properties, before focusing on the applications for mainly proteins detection, are given. Emerging use as blocking tags in nanochannels-based immunosensing systems is also covered in this review. Finally, aspects related to the analytical performance of the developed devices together with prospects for future improvements and applications are discussed.

Simple and rapid electrochemical quantification of water-stabilized HgSe nanoparticles of great concern in environmental studies.

The sensitive monitoring of mercury (II) selenide nanoparticles (HgSe NPs) is of great potential relevance in environmental studies, since such NPs are believed to be the ultimate metabolic product of the lifesaving mechanism pathway of Hg detoxification in biological systems. In this context, we take advantage of using gold-nanostructured screen-printed carbon electrodes (SPCE-Au) for the rapid, simple and sensitive electrochemical quantification of engineered water-stable HgSe NPs, as an advantageous alternative to conventional elemental analysis techniques. HgSe NPs are first treated in an optimized oxidative/acidic medium for Hg2+ release, followed by sensitive electrochemical detection by anodic stripping voltammetry (ASV). To the best of our knowledge, this is the first time that water-stable HgSe NPs are quantified using electrochemical techniques. The low limit of detection achieved (3.86 × 107 HgSe NPs/mL) together with the excellent repeatability (RSD: 3%), reproducibility (RSD: 5%) and trueness (relative error: 10%), the good performance in real sea water samples (recoveries of the analytical signal higher than 90%) and the simplicity/low cost of analysis make our method an ideal candidate for HgSe NPs monitoring in future environmental studies.