Nanotechnology and the Diagnosis of Dermatological Infectious Disease

Despite advances in diagnostics and therapeutics, infectious diseases continue to be a major cause of morbidity and mortality, surpassing cardiovascular diseases and cancer.¹ Accurate identification of causative pathogens is critical to prevent the spread of infectious diseases and to deliver appropriate and timely therapy. However, conventional diagnostic techniques such as microscopy, immunoassays (including fluorescent immunoassays, agglutination tests, and enzyme-linked immunosorbent assays [ELISA]), and polymerase chain reaction (PCR) have limitations.^2-4 For example, microscopy-based methods require samples with high pathogen concentrations as well as long incubation periods to yield results. Moreover, some microorganisms, especially viruses, are not easily grown in culture, making their identification even more challenging. Immunoassays and PCR are highly sensitive, however they require extensive sample preparation, utilize expensive reagents, and have long readout times.^3,4 These limitations also restrict the use of these conventional techniques to clinical laboratories, and render them impractical for use in the field or in developing countries where resources are scarce and infectious diseases are a major source of morbidity.⁴

Nanotechnology offers many advantages for pathogen detection and identification. Through surface modifications, nanoparticles can be tailored to bind microbial surface markers, nucleic acids, and toxins. Combining these nanoparticles with novel detection technologies has led to the development of faster, more sensitive, and more economical diagnostic assays.^3,4 This review will focus on the diagnostic advances that utilize fluorescent, metallic, and magnetic nanomaterials (Table 1), highlighting their potential applications in the diagnosis of infectious diseases, specifically infectious dermatological conditions.

Fluorescent Nanomaterials
Fluorescent labeling can be used to identify and track specific molecules of interest,⁵ however, conventional techniques that utilize organic dyes and fluorescent proteins are limited by broad emission spectra, fast photobleaching, and low signal-to-noise ratios. In contrast, fluorescent nanoparticles (NPs) are filled with thousands of organic fluorophores and thus overcome the inadequacies of conventional fluorescent markers.⁶ Thus, fluorescent NPs represent a new class of photostable, highly-sensitive tags for labeling of biological samples.⁴

Quantum Dots
Quantum dots (QDs) are colloidal semiconductor nanocrystals composed of materials in the periodic groups II-VI (eg, CdSe) or III-V (eg, InP).^4,5,7 Less than 10 nm in diameter, QDs offer significant advantages over conventional markers including narrow emission spectra, high resistance to degradation, and broad excitation spectra that can be adjusted based on size and composition to wavelengths from the ultraviolet to near infrared regions.^3,8

Many studies have investigated the potential of QDs for imaging and detection of infectious pathogens including viruses, bacteria, and fungi. The identification of Respiratory Syncytial Virus (RSV) both in vitro and in vivo was accomplished through the coupling