Handheld Device Adapted to Smartphone Cameras for the Measurement of Sodium Ion Concentrations at Saliva-Relevant Levels via Fluorescence

Abstract

The use of saliva sampling as a minimally-invasive means for drug testing and monitoring physiology is a subject of great interest to researchers and clinicians. This study describes a new optical method based on non-axially symmetric focusing of light using an oblate spheroid sample chamber. The device is simple, lightweight, low cost and is easily attached to several different brands/models of smartphones (Apple, Samsung, HTC and Nokia) for the measurement of sodium ion levels at physiologically-relevant saliva concentrations. The sample and fluorescent reagent solutions are placed in a specially-designed, lightweight device that excludes ambient light and concentrates 470-nm excitation light, from a low-power photodiode, within the sample through non-axially-symmetric refraction. The study found that smartphone cameras and post-image processing quantitated sodium ion concentration in water over the range of 0.5–10 mM, yielding best-fit regressions of the data that agree well with a data regression of microplate luminometer results. The data suggest that fluorescence can be used for the measurement of salivary sodium ion concentrations in low-resource or point-of-care settings. With further fluorescent assay testing, the device may find application in a variety of enzymatic or chemical assays.

Feasibility Study of an Optical Caustic Plasmonic Light Scattering Sensor for Human Serum Anti-Dengue Protein E Antibody Detection

“…Detection methods in developing countries for tropical diseases need to be accurate and performed in a timely manner to prevent disease. The approach described in this study aimed to combine gold nanoparticle conjugates with a portable (smartphone) sensor for detecting with a high level of sensitivity at low antigen levels [ 8 ]. The first part of the study described was the calibration of the gold nanoparticle size ( Figure 1 ).…”

“…A previously described handheld smartphone-enabled optical caustic light scattering sensor was used to capture images of samples in an oblate spheroid chamber [ 5 , 8 ]. A 532 nm green photodiode (Industrial Fiber Optics, Tempe, AZ, USA) illuminated the sample chamber at a 90° angle from a Nokia Lumia 920 (Nokia, Espoo, Finland) smartphone camera lens.…”

Smartphone‐based clinical diagnostics: towards democratization of evidence‐based health care

“…Similarly, the concentration of lactate in oral fluids and sweat samples have been measured via HRP‐induced colorimetric and chemiluminescent reactions coupled to smartphones , as well as sensitive measurements of pH and Na + ions in sweat and saliva samples (Fig. a) . For instance, for the detection of Na + ions, Lipowicz et al .…”

“…For instance, for the detection of Na + ions, Lipowicz et al . adopted a sample microfluidic chamber with a special geometrical shape and a holographic diffraction grating film, which allowed to focus the excitation light and hence improve the fluorescence signals from the samples. Similar approaches have been reported for electrolytes such as potassium, chloride and calcium .…”