Gelatin-Based Microfluidic Channel for Quantitative E. Coli Detection Using Blue Fluorescence of 4-Methyl-Umbelliferone Product and a Smartphone Camera

Escherichia coli
(E. coli)
is a foodborne pathogen that can produce potent toxins, causing severe illnesses due to contaminated food and water consumption. This research has utilized a fluorescence measurement to quantify
E. coli
colonies from blue fluorescence emitted by 4-methyl-umbelliferone (4MU). The 4MU is the product of the catalytic reaction between beta-D-glucuronidase (GUD) secreted by multiple strains of
Escherichia coli
and its substrate 4-methylumbelliferyl-beta-D-glucuronide (MUG). Here, we apply the 4MU enzymatic reaction and propose simple instrumentation for label-free, real-time,
in-situ, and
quantitative
E. coli
measurement. The detection platform consists of a smartphone camera, an ultraviolet light source for fluorescence excitation, and MUG suspended microfluidic channels. The underlining mechanism for the proposed
E. coli
measurement is the passive diffusion process of the MUG secreted by
E. coli
and the GUD suspended in the gelatin, forming the blue fluorescence 4MU product in the channels. We have also proposed a cost-effective and eco-friendly fabrication method for preparing the MUG suspended gelatin microfluidic channels using a laser printer. Gelatin is an ultraviolet light-absorbing material in nature, providing an embedded optical filter. Here, we demonstrate that a smartphone camera can be utilized to image the fluorescence emission of the 4MU excited by the ultraviolet light in the gelatin film. The proposed
E. coli
detection technique allows the amount of
E. coli
colonies to be quantified without liquid sampling, cell-culturing, inoculation, and sophisticated equipment. Furthermore, the proposed method has a trade-off between response time and detection limit.