A <i>Blautia producta</i> specific gFET-based aptasensor for quantitative monitoring of microbiome quality

The use of health-relevant bacteria originating from human microbiomes for the control or therapy of diseases, including neurodegenerative disorders or diabetes, is currently gaining increasing importance in medicine. Directed and successful engineering of microbiomes <i>via</i> probiotic supplementation requires subtle, precise as well as, more importantly, easy, fast and convenient monitoring of its success, <i>e.g.</i>, in patients' gut. Based on a previously described polyclonal SELEX aptamer library evolved against the human gut bacterium <i>Blautia producta</i>, we finally isolated three individual aptamers that proved their performance concerning affinity, specificity and robustness in reliably labeling the target bacterium and in combination with "contaminating" control bacteria. Using biofunctionalization molecules on gFETs, we could specifically quantify 10¹-10⁶ cells per mL, retrace their number in mixtures and determine aptamer <i>K</i>_d-values around 2 nM. These measurements were possible even in the context of a real human stool sample. Our results qualify gFETs in combination with BL2, BL7 and BL8 aptamers as a promising foundation for the construction of respective sensing devices, which will open new avenues towards developing an intended monitoring technique for probiotic therapy and microbiome engineering approaches.