Miniaturized pH Holographic Sensors for the Monitoring of Lactobacillus casei Shirota Growth in a Microfluidic Chip

Abstract

Bioreactors have been used both to develop new, and to improve bioprocess yields for, biopharmaceutical products. However, efforts to miniaturize bioreactors, in order to save costs and accelerate process development times, have been limited by the lack of on-site monitoring capabilities available at such scales. In this study, small volume (3 nL) nonconsumptive holographic sensors were integrated into a glass-PDMS microfluidic chip to monitor via a blue-shift in the resultant holographic replay wavelength, the change in pH during microbial growth of Lactobacillus casei (L. casei) Shirota. Within the optimal growth pH range of L. casei, the accuracy of the miniaturized pH sensors was comparable to that of a conventional pH meter. Conceivably, this approach could be extrapolated to an array of miniaturized holographic sensors sensitive to different analytes, and thereby paving the way for reliable, real-time, noninvasive monitoring of microorganisms in a nanobioreactor.

Fabrication, Potentiometric Characterization, and Application of Screen-Printed RuO2 pH Electrodes for Water Quality Testing

“…Thus, the availability of cheap, accurate, and stable pH sensors is of high importance. pH sensors, developed in the last decades, vary in detection principles, sensing materials, and fabrication methods [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. One of the most effective and inexpensive techniques of pH detection is the potentiometric method where the pH of the sample is determined by measuring the potential difference between a pH-sensitive electrode and a reference electrode.…”

Holographic Sensors in Biotechnology

“…Over a pH range from 3.0 to 6.0, the peak wavelength of the holographic sensor shifted from 450 to 540 nm. The sensor has accuracy comparable to a standard [120] Copyright 2019, American Chemical Society.…”

“…A holographic pH sensor was fabricated by Chan et al with the purpose of using change in pH attributed to bacterial metabolism of glucose into lactic acid for monitoring microorganism, Lactobacillus casei Shirota, growth. [120] Gel precursor solution consisting of a monomer: HEMA, cross-linker: EGDMA, solvent: isopropyl alcohol (IPA), pH-sensitive moiety: 2-(trifluoromethyl acrylic acid) (TFMPA), photoinitiator: 2-2-dimethoxy-2-phenylacetophenone (DMPA) and polymerization inhibitor: hydroquinone (HQ) was prepared, introduced between the sample substrate and the COC (cyclic olefin copolymer) cover, and polymerized under UV light through a chrome-glass photomask (Figure 17a). The diffraction gratings were generated via the in situ formation of Ag 0 nanoparticles, by diffusing silver perchlorate and lithium bromide into the gel matrix and exposure to a 532 nm continuous wave SLM laser.…”

“…a) Schematic of the setup for hydrogel fabrication; b) Representation of the sensor function in reflection mode; c-i) Visual representation of 3D elevation of holographic sensor after fabrication, ii) Photograph of holographic sensor taken by CMAS camera whilst immersed in pH 6.0 McIIvaine buffer; d) Colorimetric response observed upon exposure of holographic gratings to Lactobacillus casei Shirota. Reproduced with permission [120]. Copyright 2019, American Chemical Society.…”

Plasmonic Elastic Capsules as Colorimetric Reversible pH‐Microsensors

“…When corrosion occurs in a material, damages start from randomly located microscopic sites, where pH has already decreased . When biofilms develop, bacteria change phenotypes and secrete substances that result in a local decrease in pH . In the case of teeth, the more acidic environment causes local demineralization and is responsible for painful cavities .…”