Abstract
On-chip integration of optical detection units into the microfluidic systems for online monitoring is highly desirable for many applications and is also well in line with the spirit of optofluidics technology–fusion of optics and microfluidics for advanced functionalities. This paper reports the construction of a UV-Vis spectrophotometer on a microreactor, and demonstrates the online monitoring of the photocatalytic degradations of methylene blue and methyl orange under different flow rates and different pH values by detecting the intensity change and/or the peak shift. The integrated device consists of a TiO2-coated glass substrate, a PDMS micro-sized reaction chamber and two flow cells. By comparing with the results of commercial equipment, we have found that the measuring range and the sensitivity are acceptable, especially when the transmittance is in the range of 0.01–0.9. This integrated optofluidic device can significantly cut down the test time and the sample volume, and would provide a versatile platform for real-time characterization of photochemical performance. Moreover, its online monitoring capability may enable to access the usually hidden information in biochemical reactions like intermediate products, time-dependent processes and reaction kinetics.
Highlights
A laser is used as the light source for the online monitoring module, and the concentration change can be determined by measuring the intensity change of transmittance at 664 nm
The Beer-Lambert law[20,21] is employed to calculate the absorbance, which is given by, A = −log10T = −log10I/I0 = εcl where A is absorbance, T is transmittance, I and I0 are the light intensity of incident light and transmittance light, respectively, ε is the molar absorptivity with units of L mol−1 cm−1, c is the concentration of the compound in solution, expressed in mol L−1, l is the path length of the sample in the flow cells
The imperfection of our on-chip UV-Vis spectrophotometer may be attributed to the non-monochromaticity of the laser point light, the fabrication error, the concentration inaccuracy and the difference of test conditions
Summary
Microreactors (e.g., fast reaction speed, save of the solution volume). the sample solutions are usually sensitive to environment changes, and the process of first collection and measurement complicates the experimental operations and brings errors. A laser is used as the light source for the online monitoring module, and the concentration change can be determined by measuring the intensity change of transmittance at 664 nm For the latter, methyl orange (MO) is used as the model since its characteristic absorption peak is shifted with the pH value and the photoreaction process. A broadband light source is necessary to trace the wavelength shifts and the intensity changes of absorption peaks These two detection modes are suitable for most of the biomedical and chemical analyses and the successful demonstration will showcase the versatility of the on-chip UV-Vis spectrophotometer for integration with other microfluidic systems
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