Smartphone Spectrometers

Abstract

Smartphones are playing an increasing role in the sciences, owing to the ubiquitous proliferation of these devices, their relatively low cost, increasing processing power and their suitability for integrated data acquisition and processing in a 'lab in a phone' capacity. There is furthermore the potential to deploy these units as nodes within Internet of Things architectures, enabling massive networked data capture. Hitherto, considerable attention has been focused on imaging applications of these devices. However, within just the last few years, another possibility has emerged: to use smartphones as a means of capturing spectra, mostly by coupling various classes of fore-optics to these units with data capture achieved using the smartphone camera. These highly novel approaches have the potential to become widely adopted across a broad range of scientific e.g., biomedical, chemical and agricultural application areas. In this review, we detail the exciting recent development of smartphone spectrometer hardware, in addition to covering applications to which these units have been deployed, hitherto. The paper also points forward to the potentially highly influential impacts that such units could have on the sciences in the coming decades.

Keywords: environmental monitoring; food quality inspection; low cost scientific instrumentation; medical diagnostics; smartphone spectrometers; smartphone spectroscopy.

Figure 1

Smartphone based eye examination of a blind woman in Kenya. This work is being performed by the PEEK Vision Foundation [3,4]. ©Rolex/Joan Bardeletti.

Figure 2

The rapid recent escalation in interest in smartphone spectrometers is evidenced by an upturn in articles on this topic in the journal literature. For reference a similar uptake in attention is apparent in respect of the earlier adoption of smartphone imaging. Please see main text for further detail.

Figure 3

Sample schematics showing the generic operating principles of some transmissive grating smartphone spectrometer designs: (A) a configuration involving a pinhole, spherical then cylindrical lens [30,31], in this case shown with a photonic crystal resonant reflection assembly placed in the optical path [30]; in (B) a similar approach is adopted, but with evanescent wave absorption measured in the medium surrounding the prism [31]; (C) shows a system for measurement of fluorescence spectra, transmitted to the spectrometer, via an optical fibre [33]; in (D) absorbance is monitored within a cuvette, with two spherical lenses and a pinhole used to filtered out scattered light and couple radiation to the spectrometer; in this case a DVD section was also used as the diffraction grating [34]. Please see the main text for further detail.

Figure 4

Sample developed reflective grating smartphone spectrometer concepts: (A) a straightforward protocol applied in both fluorescence and absorption modalities with diffraction achieved using either a CD or in-house constructed diffraction grating [38,39]; (B) an endoscopic approach, whereby probe type sampling was demonstrated, for example in food quality determination [40]; finally (C) a 3D printed Czerny turner design, incorporating a modified Raspberry Pi camera as the detector, which is based on a smartphone sensor [41]. The ray colouration provides a sense of the dispersion within these units, whereby the red rays signify the longer wavelengths, and the blue rays, the shorter ones. Please see main text for further details.

Figure 5

Raspberry Pi camera-based spectrometer applied to measurements of sulphur dioxide gas release from Cotopaxi volcano, Ecuador.