  This paper reports on the development of a novel CMOS device employing
lead-sensing bacteria to assay lead in drinking water. The objective of the
PlomBOX project is to develop a low-cost sensor ({\pounds}10) which can
expedite access to on-demand assay methods and thus help mitigate lead intake
through contaminated drinking water. The project follows three development
paths: a) Certain bacteria can fluoresce or change colour when in the presence
of lead. A genetically modified strain of Escherichia coli sensitive to lead
concentrations up to 10 ppb is being developed. This constitutes the biosensor
that fluoresces in proportion to the presence of lead. b) Bacteria response is
imaged using a microprocessor (ESP32) with a camera module. This constitutes
the optical metrology component of the PlomBOX. c) Data acquisition and control
of the PlomBOX is achieved through a Bluetooth connection with the PlomApp, a
custom-developed mobile phone application. Data are sent from the PlomApp to a
database where a bespoke automated analysis software provides a result of the
lead concentration in a sample of water. This paper reports on the
instrumentation challenges of developing the electronics for the PlomBOX and on
the first prototype.
