Hyperspectral spatially offset Raman spectroscopy in a microfluidic channel

Abstract

Spatially offset Raman spectroscopy (SORS) enables one to distinguish chemical fingerprints of top and subsurface layers. In this paper, we apply SORS to a microfluidic two-layer system consisting of transparent liquid in a microchannel as the surface layer and microfluidic PDMS chip material as the sublayer. By using an imaging spectrograph connected to a microscope, we perform hyperspectral SORS acquisitions. Furthermore, the focus position z is translated. Thus, we combine the two methods of hyperspectral SORS and defocusing micro-SORS, which leads to an integral characterization of the layered system. The collected top and subsurface layers of Raman scattering at the optical axis (zero spatial offset) largely depends on the focus position z. However, the spatially offset Raman scattered intensity from the subsurface layer is constant for a large range of focus positions z. We claim that there is potential for internal referencing and alignment reproducibility. We demonstrate these findings experimentally in a microfluidic scenario where a 16 µm deep channel is filled with an aqueous hemoglobin solution. Our observation enables consistent concentration measurements in small-volume liquid samples.

Spatially offset Raman spectroscopy

“…Other application areas not covered extensively in this section include those in the polymer sciences 85,86 , petrochemical 87 and chemical sciences 88 and manufacture 89 , geology and mineralogy 90,91 , biology 92 and cosmetics 93 .…”

In situ non-invasive Raman spectroscopic characterisation of succinic acid polymorphism during segmented flow crystallisation

“…This final point can be explained through a scan rate of 4 s per data collection of slugs moving at 18 slugs per min under the probe, the data acquisition time resulting probing 0.6 slugs every measurement; random fluctuations in either data acquisition start point or air and solution slug length could lead to most of the data collection during the low intensity regime, being collected from air slugs, while only catching small (low crystal slurry density portions) of a solution slug. Future avenues for opportunity would be to employ spatially offset Raman spectroscopy (SORS), 28 which would allow spectra to be obtained without the masking effect of the reactor wall, as well as synchronising the flow and the data collection regimes.…”

Label‐Free Blood Typing by Raman Spectroscopy and Artificial Intelligence

“…Positions that were spatially offset from the focus of the laser excitation spot collect Raman scattered light from sample volume that was not in focus with the focal plane of the microscope. [ 9 ] The capillary was aligned perpendicular to the optical axis of the microscope objective with the center of the capillary in the xy ‐plane. Raman signal from the fused silica capillary walls was suppressed by focusing the excitation laser along the z direction until fused silica Raman peaks disappear and signal from the blood samples was maximized.…”

“…RS has been used for a wide range of applications in bioanalytics and blood analysis [4,5] including detection of glycated hemoglobin for diagnosis of diabetes, [6] in vivo measurements of oxygen saturation of hemoglobin, [7,8] and point of care detection of hemolysis. [9][10][11][12] RS has shown a potential to recognize distinct features of the different erythrocyte blood group antigens and thus distinguish between ABO blood group antigens, but has so far relied on comprehensive sample preparation steps applied to isolate specific substances or components of the blood, thus limiting the throughput and the resulting dataset sizes. A laser tweezers Raman spectroscopy (LTRS) system has been proposed to probe single trapped erythrocytes, [13] and surface-enhanced Raman scattering (SERS) spectroscopy on purified globulins from blood plasma have been used to discriminate ABO blood types.…”