Abstract:
Low-cost, portable biosensors for the detection of Escherichia coli (E. coli) in
water were investigated. The operating principle of various biosensors is discussed
at the hand of a biosensor model. These methods, including electrical
and optical methods, are evaluated for use in low-cost sensors. An electrically
and optically based biosensor are compared.
An electrochemical impedance biosensor that detects bacteria using non-linear
AC harmonics is evaluated. Various electrode geometries and materials patterned
on glass chips were tested. Ionic solutions were tested and a sensitivity
of 0.01 mg/L for NaCl, KCl and MgCl2 was achieved. E. coli B44 was tested,
and bacterial concentration curves for the sensor was derived. The limit of
detection (LOD) of the sensor was 1.1 1010 CFU/ml, and the response time
less than 4 minutes.
A ber-optic biosensor, operating using evanescent wave modulation, was
tested. A low-cost testing method, using simple optoelectronics, was derived
and hand-made bers were manufactured. The bers were immobilised with
primary anti-E. coli antibodies by covalent attachment with a (3-Glycidyl
oxypropyl) trimethoxysilane (GPS) crosslinking agent. The immobilisation
e ciency was determined using Wide Field Fluorescence microscopy. Bacterial
concentrations (E. coli DH5 ) were tested, and bacteria was successfully
detected. The LOD of the sensor was 3 107 CFU/ml, and the response time
less than 120 minutes.
The two sensors are compared and evaluated for use in low-cost, portable biosensing
systems for water testing. Recommendations for future development
of a low-cost, portable biosensing prototype is discussed, including a system
model and possible speci cations. Possible applications for future biosensor
development is discussed in detail.
