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. 2015 Jun 2;2(2):122-138.
doi: 10.3390/bioengineering2020122.

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

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

Michelle Lipowicz et al. Bioengineering (Basel). .
Free PMC article

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.

Keywords: fluorescence; low-resource settings; non-axially-symmetric focusing; oblate spheroid; saliva; smartphone; sodium ions.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
3D-printed housing with blue LED light (located inside housing) and detachable, 3D-printed iPhone 4 holder (shown without transmission grating). The system quickly connects different smartphone models to the housing, using an Archimedes screw design, while minimizing ambient light.
Figure 2
Figure 2
Image illustrating the effect of combining refractive chromatic dispersion with diffraction using a transmission grating in order to separate excitation and emission wavelengths prior to digital image processing.
Figure 3
Figure 3
Smartphone fluorimeter spectra resolving the excitation and emitted light and compared to graphed data from the distributor of Sodium Green Tetra [8].
Figure 4
Figure 4
Linearized plot of fluorescence with a 520-nm (top equation and R2 value) and 590-nm emission filter (equations to the left of the lines and R2 value are measured using the manufacturer’s supplied software, FluoroPLUS, TiterTek Instruments, Huntsville, AL, 2009). The other data represent the red and green integrated intensity values as measured using the integrated density of the red image channel (RED INTDEN) and the same area for the green image channel (GREEN INTDEN). Data where a holographic grating is used in front of the camera lens are designated as Red DFG and Green DFG respectively. The dotted trend line and lower-right equation are for the Green DFG, which had the best correlation when compared to the microplate reader, especially at the lower sodium ion concentrations. Relative fluorescence readings are determined based on normalizing with respect to the fluorescence measured at a 10 mM initial sodium ion concentration for each instrument. Simulated saliva (SS1) is used for the data at a 5 mM Na ion concentration.
Figure 5
Figure 5
Another comparison series of the luminometer and smartphone fluorimeter as a function of initial sodium ion concentration along with the best-fit linear correlations are shown. All smartphones were equipped with a holographic grating, and the green channel was used to calculate fluorescence based on integrated density measurements. Relative fluorescence readings are used based on normalizing with respect to the fluorescence measured at a 10 mM initial sodium ion concentration.
Figure 6
Figure 6
(a) The color separation of white light through a diffraction grating film. (b) (Top) Chromatic dispersion for a white light point source emitting from a focal zone inside the oblate spheroid due to refraction (color separation exaggerate for clarity) and (bottom) two rays refracting from a blue light source to help clarify that there is a focal zone within the sample chamber. The image in (a) was adapted from Cmglee (GFDL (http://www.gnu.org/copyleft/fdl.html)), via Wikimedia Commons, in order to provide a visual reference to compare with the chromatic dispersion effect shown in (b).
Figure 7
Figure 7
Equations to simulate intensity profiles for regular and elliptical axicon intensity profiles at a particular axial distance Z ≤ focal length [23,24]. The function S is the Mathieu sine function, and k is the angular wavenumber.
Figure 8
Figure 8
The intensity profiles are plotted using equations that simulate the spherical and spherical with coma aberrations at the optical caustic focal length [20,30]. In the right panel, the parameter ɛ is the eccentricity of the oblate spheroid, and as in Figure 4, k is the angular wavenumber.
Figure 9
Figure 9
Images of a spherical and an oblate spheroid sample chamber using a red light (620 nm) source in direct line with the camera sensor. The sample chambers are filled with water. The top panels show the images and a histogram of the pixel intensities for the RGB images. 3D renderings of the data and inserts showing 2D ray tracings are given in the lower panels for qualitative comparisons to the graphs in Figure 8.
Figure 9
Figure 9
Images of a spherical and an oblate spheroid sample chamber using a red light (620 nm) source in direct line with the camera sensor. The sample chambers are filled with water. The top panels show the images and a histogram of the pixel intensities for the RGB images. 3D renderings of the data and inserts showing 2D ray tracings are given in the lower panels for qualitative comparisons to the graphs in Figure 8.

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References

    1. Marques M., Loebenberg R., Almukainzi M. Simulated biological fluids with possible application in dissolution testing. Dissolution Technol. 2011;18:15–28. doi: 10.14227/DT180311P15. - DOI
    1. Life Technologies, Sodium Green™ Indicator in The Molecular Probes Handbook. [(accessed on 2 March 2015)]. Available online: http://www.lifetechnologies.com/us/en/home/references/molecular-probes-the-handbook/indicators-for-na-k-cl-and-miscellaneous-ions/fluorescent-na-and-k-indicators.html.
    1. Kaushik A., Vasudev A., Arya S.K., Pasha S.K., Bhansali S. Recent advances in cortisol sensing technologies for point-of-care application. Biosens. Bioelectron. 2014;53:499–512. doi: 10.1016/j.bios.2013.09.060. - DOI - PubMed
    1. Motamayel Ahmadi F., davoodi P., Dalband M., Hendi S.S. Saliva as a mirror of the body health. DJH. 2010;1:1–15.
    1. Pels E. Oral hygiene status and selected saliva biomarkers in children with acute lymphoblastic leukaemia during anticancer therapy. J. Leuk. 2013 doi: 10.4172/2329-6917.1000115. - DOI
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