Compact characterization of liquid absorption and emission spectra using linear variable filters integrated with a CMOS imaging camera

Abstract

A compact analysis platform for detecting liquid absorption and emission spectra using a set of optical linear variable filters atop a CMOS image sensor is presented. The working spectral range of the analysis platform can be extended without a reduction in spectral resolution by utilizing multiple linear variable filters with different wavelength ranges on the same CMOS sensor. With optical setup reconfiguration, its capability to measure both absorption and fluorescence emission is demonstrated. Quantitative detection of fluorescence emission down to 0.28 nM for quantum dot dispersions and 32 ng/mL for near-infrared dyes has been demonstrated on a single platform over a wide spectral range, as well as an absorption-based water quality test, showing the versatility of the system across liquid solutions for different emission and absorption bands. Comparison with a commercially available portable spectrometer and an optical spectrum analyzer shows our system has an improved signal-to-noise ratio and acceptable spectral resolution for discrimination of emission spectra, and characterization of colored liquid’s absorption characteristics generated by common biomolecular assays. This simple, compact, and versatile analysis platform demonstrates a path towards an integrated optical device that can be utilized for a wide variety of applications in point-of-use testing and point-of-care diagnostics.

Portable Spectroscopy

“…184,185 Case 4 has largely been explored in university and other research institutions to construct portable clinical analyzers. [513][514][515][516][517][518][519][520][521][522][523][524][525][526][527][528][529] The fluorescence and colorimetric test reagents for clinical assays and analyses are well-known and widely available. In principle, therefore, interfacing microfluidics and a wavelength-selective device to a smartphone camera, with appropriate software, produces a mobile clinical analyzer with built-in communications abilities.…”

Simple but effective: strong efficiency boost for a linear variable filter-based spectrometer

“…To date, several types of LVF have been developed, including metal-dielectric 13 and all-dielectric structures. [14][15][16][17][18][19][20][21][22] The latter ones became more prevalent and are already commercially available, 16,17 with wavelength ranges covering, e.g., 320 to 560, 450 to 850, and 800 to 1100 nm, 16 or infrared (IR) regions, such as 0.9 to 1.70 or 2.5 to 5.0 μm. 17 Numerous applications and devices based on LVFs have been reported, such as gas 19 and liquid 20 measurements, thin-film measurements, 21 broadband spectrometers for current NASA space missions, 22 order sorting filters for commercial grating spectrometers, 24 multispectral and hyperspectral imaging, 25,26 commercially available LVF monochromators, 27 and hyperspectral video cameras.…”

“…Depending on the specific arrangement, this principle is multiple times more efficient than the conventional approach in which the white input light bundle is expanded to illuminate the entire LVF dispersive direction, as was realized, for example, in Ref. 20. Figure 1(b) shows an example using nine subbands by applying a matrix combining 3 × 3 beamsplitters to illuminate filter arrays.…”

“…Filter-based spectrometers can have an extremely compact and rigid design without any moving parts, consisting of only a filter array or longitudinally variable filter placed in front of a sensor array, for example, a chargecoupled device (CCD) or complementary metal-oxide-semiconductor, to capture a spectrum in one shot. A variety of spectral filters and structures, often micrometer-sized, have been developed, such as plasmonic color filters, 4,5 photonic crystal arrays, 6 single nanowires, 7 absorptive filter arrays composed of either conventional colloidal quantum dots 8 or perovskite quantum dots, 9 Fabry-Pérot (FP) filter arrays, [10][11][12] and linear (also called "continuously") variable filters [13][14][15][16][17][18][19][20][21][22] [linear variable filters (LVFs)]. An important benefit of such types of spectrometers compared to grating-based spectrometers is the possibility of detecting a broad spectral range with high spectral resolution despite their small size.…”

Mixed-gas CH4/CO2/CO detection based on linear variable optical filter and thermopile detector array

“…Doubtlessly, both techniques will inevitably result in the increase of detector size and cost. For these reasons, many micro-optics devices have been used to construct the miniaturized NDIR multi-gas sensors, e.g., MEMS-based Fabry-Pérot (F-P) filters [18, 19], photonic crystal filters [20, 21], and linear variable optical filter (LVOF) [22, 23]…”