Development and Testing of ZnO Nanorods Based Biosensor on Model Gram-Positive and Gram-Negative Bacteria

Water is a basic human need, but many people do not have access to clean and safe drinking water. Many people die of waterborne bacterial diseases in the world. The presence of bacterial pathogens in water can be detected by using sophisticated and expensive instruments, which take extensive time for measurement. In contrast to those instrumentation, nanostructure-based devices can be used as instant and cheap bacteria sensors. This paper reports the fabrication of a sensor using ZnO nanorods for detection of two bacterial pathogens, namely Escherichia coli, which is a gram-negative bacteria and Streptococcus pneumonia, which is a gram-positive bacteria present in water at different concentrations. The fabrication of the sensor was done by growing ZnO nanorods hydrothermally on a Cu electrode. The sensor was then tested with some known concentrations of bacteria mixed in water. When bacteria mixed water sample is dropped over the sensor, the electrical resistance of the sensor varies proportionally with bacteria concentration. Maximum responses of 96% and 94.375% at room temperature and minimum detection limits of 1.12% and 1.01% were achieved for $9.15\times 10^{8}$ cells/mL of E. coli and $1.043\times 10^{9}$ cells/mL of S. pneumonia present in water, respectively. The high sensitivity and dynamic repeatability exhibited by these sensors reveal that ZnO nanorods are promising as sensitive and reliable sensors for detecting bacteria present in water.