Multi-parameter sensing platform for rumen monitoring

Abstract

Green-house gas (GHG) emissions from livestock contribute to environmental issues including global warming and climate change. There is a need to monitor parameters from animals, particularly ruminants to explore mitigation. These parameters include pH, oxidation-reduction potential (ORP) , dissolved oxygen (DO) and conductivity. Understanding these may help reduce the emission of GHGs and protect cows from diseases.
Electrochemical measurement techniques may provide solutions due to the low cost, small size, ease of integration and good accuracy. A stable reference electrode (RE) is required to provide a reference voltage and in this thesis, quasi-REs (QREs) were developed, which were also considered as Cl- sensors. Ruthenium Oxide (RuOx) pH sensors were made, showing good linearity and near-Nernstian response in phosphate-buffered saline (PBS) solution (-56.1mV/pH). Pt ring DO sensors were manufactured to measure dissolved oxygen concentration (DOC) with ±1.7% accuracy but with a limited detection range of 1-8mg/L. Conductivity sensors were developed exhibiting comparable performance (accuracies from ±0.5% to ±2.7%) to a commercial conductivity meter under laboratory test in the range 1.5-23mS/cm. ORP sensors were made from a Pt plate and showed good response with deviation <8mV from calibration solutions.
In vitro studies were carried out with three different rumen contents for the detection of Cl-, pH, ORP, and conductivity using miniaturized sensor chips. The pH sensors demonstrated good matching with the commercial meter (∆pH<0.14). ORP sensors took a few hours to stabilize and showed average ORP values of -0.099V, -0.123V and -0.07V in three rumen contents. QREs degraded rapidly in the rumen environment, giving an initial Cl- concentration of 0.04-0.054M in rumen fluid. Excellent performance was observed for the conductivity sensor. In all three samples, low deviations were detected regardless of the chip configuration. In sample #1 and sample #3 the error was within 3.7% while in sample #2 larger errors were measured, as a result of the rapid temperature change and proximity effect due to active protozoa. The conductivity sensors were capable of delivering accurate measurements after a week, demonstrating minimal influence from the biofouling effect.
Future work involves the improvement of on-chip RE and DO sensors, optimization of in vitro measurement setup and the development and encapsulation of interface circuitry and sensor chips for in vivo detection.

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Identifiers

ORCID for Zijin Fang: orcid.org/0000-0001-8656-4920

ORCID for Hywel Morgan: orcid.org/0000-0003-4850-5676

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