Purposes

To realize the idea of in-field detection, a device with remarkable convenience for monitoring environmental water pollution should be proposed. This device must be capable of determining if the specific kind of aromatic compound exists in a water sample, and perhaps more significantly, measuring specific aromatic compound’s concentration semi-quantitatively. To meet the requirement of convenience, the detection process must be fast and the result must be read with naked eyes or with user-friendly devices. As for measuring the concentration, a concentration gradient could be constructed by the pre-treating method of the device, so different response patterns may roughly reflect the concentration. All this requirements must be carefully designed with biosafety concerns.
The most challenging part of a biological detection device is the preservation method. The sensor strain we use, Escherichia coli, failed to germinate spores or gemma to resist general preservation conditions of dehydration, temperature changes and physical interference. Several approaches were designed to achieve valid maintainance benefits. Based on the fundamental designs, an advanced device with multifunctions was proposed to measure the concentration carrying potential for further improvements.

Alginate Encapsulation

Alginate is a polysaccharide consists of β-D-mannuronic acid (M) and α-L-guluronic acid (G) residues. If treated by calcium irons, G residues are cross-linked and a coat would be formed within a rather short period of time.
Alginate is frequently used as the biological encapsulation material for various organisms such as Saccharomyces cerevisiae, Escherichia coli and mammalian cells[1][2]. It came into our consideration as the encapsulating material for its outstanding specifications, which include[8]:
(1) Food grade materials which are stable and inexpensive
(2) Possibility to use every biosensor we constructed
(3) Ease to shape and manipulate
(4) Protection against environmental stresses
The alginate encapsulation successfully solve the problem of dehydration and oxidation stress upon our biosensor strains, so no reviving process is required. With the support of protective agents, the period of validity could be longer than a month in 4℃.