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.

In the last decade, the field of nanoparticle (NP) technology has attracted immense interest in bioimaging and biosensing research. This technology has demonstrated its capability in obtaining sensitive data in a noninvasive manner, promising a breakthrough in early-stage cancer diagnosis, stem cell tracking, drug delivery, pathogen detection and gene delivery in the near future. However, successful and wide application of this technology relies greatly on robust NP engineering and synthesis methodologies. The NP development steps involve design, synthesis, surface modification and bioconjugation. Each of these steps is critical in determining the overall performance of NPs. It is desirable to obtain NPs that are highly sensitive, stable, imageable, biocompatible and targetable. It is also desirable to obtain multimodal/multifunctional NPs that will enable imaging/sensing of the target using multiple imaging/sensing modalities. In this review, we focus on silica NPs that have been developed for biosensing applications and silica-based multimodal/multifunctional NPs for bioimaging applications.

A robust water-in-oil microemulsion method of making water-dispersible ultra-small (<30 nm) size fluorescent chitosan nanoparticles is reported for the first time and specific targeting of these FCNPs to human leukemia cells via aptamer recognition is demonstrated.

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