A low-cost miniature immunosensor for haemoglobin as a device for the future detection of gastrointestinal bleeding

Gastrointestinal bleeding (GIB) is a serious medical condition, which requires immediate attention to establish the cause of the bleeding. Here, we present the development of a miniaturised electrochemical impedance spectroscopy (EIS) device for the detection of GIB. The device performs EIS measurements up to 100 kHz. Following the development of an immunosensor for haemoglobin (Hb) on screen printed electrodes, the EIS device was used for detecting Hb as an early indication of bleeding. The sensor was able to detect Hb in a redox solution in a linear range between 5 μg mL^-1 and 60 μg mL^-1, with a limit of detection of 13.3 μg mL^-1. It was also possible to detect Hb in simulated intestinal fluid, without the need for a redox solution, within a range of 10 μg mL^-1 to 10 mg mL^-1 with a limit of detection of 2.31 mg mL^-1. The miniature EIS device developed in this work is inexpensive, with an estimated cost per unit of £30, and has shown a comparable performance to existing commercial tools, demonstrating its potential to be used in the future as an ingestible sensor to detect GIB. All these measurements were carried out in a purpose built flow cell with supporting hardware electronics outside the cell. Integration of the hardware and the sensing electrodes was demonstrated in pill form. This pill after integration sampling fluidics has potential to be used in detecting gastrointestinal bleeding.