New methods to identify trace amount of infectious pathogens rapidly, accurately and with high sensitivity are in constant demand to prevent epidemics and loss of lives. Early detection of these pathogens to prevent, treat and contain the spread of infections is crucial. Therefore, there is a need and urgency for sensitive, specific, accurate, easy-to-use diagnostic tests. Versatile biofunctionalized engineered nanomaterials are proving to be promising in meeting these needs in diagnosing the pathogens in food, blood and clinical samples. The unique optical and magnetic properties of the nanoscale materials have been put to use for the diagnostics. In this review, we focus on the developments of the fluorescent nanoparticles, metallic nanostructures and superparamagnetic nanoparticles for bioimaging and detection of infectious microorganisms. The various nanodiagnostic assays developed to image, detect and capture infectious virus and bacteria in solutions, food or biological samples in vitro and in vivo are presented and their relevance to developing countries is discussed.

Fluorescent nanoparticles (FNPs) have received immense popularity in cancer imaging in recent years because of their attractive optical properties. In comparison to traditional organic-based fluorescent dyes and fluorescent proteins, FNPs offer much improved sensitivity and photostability. FNPs in certain size range have a strong tendency to enter and retain in solid tumor tissue with abnormal (leaky) vasculature--a phenomenon known as Enhanced Permeation and Retention (EPR) effect, advancing their use for in vivo tumor imaging. Furthermore, large surface area of FNPs and their usual core-shell structure offer a platform for designing and fabricating multimodal/multifunctional nanoparticles (MMNPs). For effective cancer imaging, often the optical imaging modality is integrated with other nonoptical-based imaging modalities such as MRI, X-ray, and PET, thus creating multimodal nanoparticle (NP)-based imaging probes. Such multimodal NP probes can be further integrated with therapeutic drug as well as cancer targeting agent leading to multifunctional NPs. Biocompatibility of FNPs is an important criterion that must be seriously considered during FNP design. NP composition, size, and surface chemistry must be carefully selected to minimize potential toxicological consequences both in vitro and in vivo. In this article, we will mainly focus on three different types of FNPs: dye-loaded NPs, quantum dots (Qdots), and phosphores; briefly highlighting their potential use in translational research.

improve the stability of hydrogel fibers and introduce multiple functionality to hydrogel fibers.Hydrogel fibers have similar properties to the natural macromolecules in extracellular matrix (ECM) such as large surface area, high porosity, and high content of water. They have been applied in mimicking 3D ECM [28][29][30][31][32][33][34][35][36][37] for tissue engineering, sensors, [38,39] immobilizing biocatalysts, [40] sustained releasing of proteins and drugs, [41][42][43] and wound healing. [44][45][46] Among three common ways of synthesizing fibers, self-assembly, electrospinning and phase separation, electrospinning is the most versatile, simple and cost effective technique. However, the application of electrospun hydrogel fibers (EHFs) faces challenges of low stability in aqueous solutions, liability to harsh chemical conditions and limitations in further functionalization.The EHFs of one polyelectrolyte component are water soluble, all subsequent chemical reactions have to be performed under solvent-free conditions or in non-aqueous media. To stabilize fibrous hydrogels in aqueous media, thermal or vaporphase crosslinking is required which impedes their applications. Polyelectrolyte complexes have been used to improve the stability of fibrous hydrogels in aqueous solutions. [32,[47][48][49][50][51][52][53][54] A polyelectrolyte complex is formed by mixing oppositely charged polyelectrolytes such as poly(acrylic acid) (PAA) and poly(allyl amine hydrochloric acid) or PAA and chitosan (CS) in solutions with controlled polymer ratio and pH. The electrostatic interactions between partially charged polymeric chains lead to the formation of a polymer hydrogel network without covalent crosslinkers. [47][48][49][55][56][57] However, when exposed to solutions with high salt concentration and extreme pH, the disruption of the electrostatic interactions between polycations and polyanions results in the dissolution of the fibers.Functionalizing EHFs requires a simpler and more versatile method to introduce a variety of functional materials such as nanoparticles, peptides, polymers onto the fibers for various applications. Current approaches include in situ fabrication where nanoparticles or polymers/peptides are added to polymer solutions before electrospinning, and post fabrication where nanoparticles or polymers/peptides are introduced onto fibers via reactions in solutions. Post fabrication approaches are not sufficient in obtaining uniform and controlled functionalization in large scale while the amount of nanoparticles in fibers is limited by the dispersity of nanoparticles in polymer solutions in preloading fabrication approaches. [58][59][60] Therefore, Inspired by natural metal ion/ligand interactions, stable electrospun hydrogel fibers (EHFs) are produced from polyelectrolyte complexes coordinated with various metal ions. This development provides a novel and promising approach to advance hydrogel fiber applications by creating fibers with high stability in solutions and controlled interfacial reactions. The e...

In spite of their attractive features, widespread biomedical applications of CS nanoparticles are yet to be realized due to their poor stability in physiological conditions, such as in buffer system at pH 7.4. Buffer-stable chitosan-based hybrid NPs (HNPs) are reported and characterized. Buffer stability is achieved by introducing polyglutamic acid to chitosan. The effect of PGA to CS molar ratio and crosslinking on HNP integrity, buffer stability, and biodegradability are studied. Preliminary in vitro studies are carried out to evaluate targeted uptake efficiency of folate conjugated HNPs. Successful demonstration of buffer stability and cancer cell targeting by HNPs achieves important milestones for chitosan-based nanoparticle technology.

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