An all-solid-state potentiometric microsensor for real-time monitoring of the calcification process by Bacillus subtilis biofilms

Abstract

Bacillus subtilis, as a bacterium with wide-ranging applications, has been explored for CO₂ sequestration using intracellular or extracellular carbonic anhydrase (CA). However, noninvasive, real-time monitoring of CA-mediated calcium carbonate precipitation processes is scarce, especially for bacteria in seawater. We report here the use of a carbon nanotube fiber-filled glass micropipette for preparing mechanically robust ion-selective microelectrodes for in situ ion sensing. Hydrophobic carbon nanotube fibers with remarkable electrical and mechanical properties can act not only as a transduction layer but also as a self-supporting material. As a model, an all-solid calcium ion-selective microelectrode (Ca²⁺-ISμE) with a size of 20 μm was designed. The Ca²⁺-ISμE shows a Nernstian response to Ca²⁺ in 0.5 M sodium chloride within the range of 1.0 × 10⁻⁶–1.0 × 10⁻² M, and the detection limit is 4.0 × 10⁻⁷ M. The proposed microsensor allows for in situ, real-time monitoring of the calcification process by Bacillus subtilis biofilms. This work provides a simple and versatile tool to monitor biomineralization processes and reveal carbon concentration and sequestration mechanisms.