1：Experimental Design and Method Selection:

The study involved fabricating miniaturized pH holographic sensors using photolithography and holographic techniques. The sensors were based on a pH-sensitive hydrogel with embedded silver nanoparticles, and their response was monitored through changes in diffracted wavelength due to gel volume changes.

2：Sample Selection and Data Sources:

Lactobacillus casei Shirota was used as the model organism, cultured in MRS broth. Samples were taken at various time points for pH, optical density, and conductivity measurements.

3：List of Experimental Equipment and Materials:

Materials included HEMA, EDMA, TFMPA, HQ, AgClO4, DMPA, Metol, L-ascorbic acid, lithium bromide, photomasks, spacers, COC covers, optomechanical apparatus, pH and conductivity meters, monochromator, spectrophotometer, high-resolution camera, and white light interferometric profiler. Equipment was sourced from various suppliers such as Merck, Acros Organics, Mettler Toledo, PhotoniTech, Knight Photonics, iSolutions Technology, and Bruker.

4：Experimental Procedures and Operational Workflow:

The hydrogel was polymerized on a silanized glass slide using UV exposure through photomasks, followed by hologram fabrication with a 532 nm laser. The sensors were integrated into a PDMS-glass microfluidic chip. Sensor interrogation involved a customized setup with a Xenon light source, fiber optics, CMOS camera, and spectrometer to measure the holographic signal. Calibration was done using McIlvaine buffers, and L. casei growth was monitored by introducing aliquots into the chip.

5：Data Analysis Methods:

Data analysis included normalization of wavelength spectra, application of the Henderson-Hasselbalch equation for pH prediction, and statistical analysis of sensor responses. Color changes were analyzed using RGB-to-xyY transformations and plotted on CIE chromaticity diagrams.