O 2 -Sensitive Inks for Measuring Total (Aerobic) Viable Count Using Micro-Respirometry.

The popular method of micro-respirometry (μR) for measuring total viable (aerobic) count (TVC) utilises luminescence-based O₂ sensors that are difficult to fabricate and therefore expensive. A simple method is described for making inexpensive, ink-based potential substitutes that utilise the same O₂-sensitive dyes. The sensitivity of such inks is readily increased by using dyes with a long lifetime in the absence of O₂, τ_o, and/or an ink resin/polymer with a high O₂ permeability, P_m(O₂). Response modelling of the μR-based TVC system and subsequent testing using a range of O₂ sensors of different sensitivity show that there is little to be gained by making the O₂ sensor either very sensitive or insensitive, and that the best O₂ sensors are dyes such as Pt(II) tetraphenyltetrabenzoporphyrin (PtBP), with τ_o = ca. 40–50 μs. Further work shows that a simple-to-make PtBP ink can be used as a direct replacement for the expensive O₂ sensor used in commercial instruments for measuring TVC based on μR. In addition, the PtBP can be replaced by an even less expensive O₂-sensitive dye, Pt(II) meso-tetra(pentafluorophenyl)porphyrin (PtTFPP). The potential use of inexpensive O₂-sensitive inks as an alternative to any expensive commercial counterpart based on the same O₂-sensitive dye is discussed briefly. [ABSTRACT FROM AUTHOR]