11/05/2026
By Thomas Dugan

The Francis College of Engineering, Department of Electrical and Computer Engineering, invites you to attend a doctoral dissertation defense by Guoqiang Cui, titled “Development, Integration, and Cross-Sensitivity Analysis of a Multiparameter Optical Fiber Sensing System for Bioreactor Monitoring.”

Details

  • Date: November 17, 2026
  • Time: Noon
  • Location: Perry Hall, Room 315

Committee members

  • Xingwei Wang, professor, Electrical & Computer Engineering, University of Massachusetts Lowell
  • Xuejun Lu, professor, Electrical & Computer Engineering, University of Massachusetts Lowell
  • Seongkyu Yoon, professor, Chemical Engineering, University of Massachusetts Lowell
  • Taehong Kwon, senior scientist, Sartorius Stedim North America Inc., Marlborough, Massachusetts

Abstract

Real-time monitoring of pH, dissolved oxygen (DO), and temperature is important for maintaining controlled conditions in bioreactors. This dissertation investigates the development, integration, and cross-sensitivity of optical fiber sensing approaches for these three process variables. The research advances from separately characterized sensing elements to integrated three-parameter measurement and an initial framework for quantifying non-target-variable interference.

A PDMS/FEP-packaged fiber Bragg grating (FBG) temperature sensor was developed as an independently interrogated component for subsequent integration. Across three independently fabricated sensors, packaging increased mean sensitivity from 11.09 ± 0.21 to 30.41 ± 0.53 pm/°C, with 99.18 ± 1.43% sensitivity retention after one nominal 121 °C autoclave cycle. Stirring and 24 h tracking experiments characterized its operating behavior.

An optical frequency domain reflectometry (OFDR)-interrogated hydrogel-coated fiber was investigated as an initial pH sensing approach. Its sensitivity was 1.94 GHz/pH over pH 4–11 and remained 1.91 GHz/pH after one steam-autoclave exposure. A proof-of-concept Chinese hamster ovary (CHO) shake-flask experiment demonstrated agreement with a commercial biochemical analyzer. Preliminary stirred-tank trials indicated susceptibility of the strain-mediated response to agitation-associated mechanical disturbances, motivating a chemically responsive pH measurement strategy for integration.

The integrated assembly combined HPTS-IP and Erythrosin B indicator regions with the packaged FBG. Four independently prepared devices underwent device-specific calibration over pH 6–8, DO 30–100% air saturation, and 30–40 °C. Independent validation produced RMSE ranges of 0.0676–0.1151 pH, 0.8464–1.0243 DO percentage points, and 0.0427–0.0703 °C. All three channels were available at 13 hourly checkpoints over a 12 h experiment in stirred phosphate buffer.