Fluorescent Imaging of Single Nanoparticles and Viruses on a Smart Phone

TLDR

Optical imaging of nanoscale objects is challenging because subwavelength dimensions reduce detection signal‑to‑noise ratio and contrast. The authors present a field‑portable smartphone fluorescence microscope that uses a lightweight opto‑mechanical attachment to image individual nanoparticles and viruses. The device employs a 450 nm laser diode with ~75° oblique excitation, a long‑pass filter to block excitation light, a 2× external lens, and a translation stage for focus, and was tested by imaging 100 nm fluorescent particles and fluorescently labeled human cytomegaloviruses with size validation by SEM. The ~186 g attachment enables specific, sensitive imaging of subwavelength objects such as bacteria and viruses, offering a valuable platform for nanotechnology practice and viral load measurements in remote, resource‑limited settings.

Abstract

Optical imaging of nanoscale objects, whether it is based on scattering or fluorescence, is a challenging task due to reduced detection signal-to-noise ratio and contrast at subwavelength dimensions. Here, we report a field-portable fluorescence microscopy platform installed on a smart phone for imaging of individual nanoparticles as well as viruses using a lightweight and compact opto-mechanical attachment to the existing camera module of the cell phone. This hand-held fluorescent imaging device utilizes (i) a compact 450 nm laser diode that creates oblique excitation on the sample plane with an incidence angle of ~75°, (ii) a long-pass thin-film interference filter to reject the scattered excitation light, (iii) an external lens creating 2× optical magnification, and (iv) a translation stage for focus adjustment. We tested the imaging performance of this smart-phone-enabled microscopy platform by detecting isolated 100 nm fluorescent particles as well as individual human cytomegaloviruses that are fluorescently labeled. The size of each detected nano-object on the cell phone platform was validated using scanning electron microscopy images of the same samples. This field-portable fluorescence microscopy attachment to the cell phone, weighing only ~186 g, could be used for specific and sensitive imaging of subwavelength objects including various bacteria and viruses and, therefore, could provide a valuable platform for the practice of nanotechnology in field settings and for conducting viral load measurements and other biomedical tests even in remote and resource-limited environments.