4.3 Biomimetic Chemical Sensors

౪

93

Figure 4.10: Twelve different fluorescence monomers in a PEG-block-PLL polymer bind gut bacteria differ-

ently. The fluorescence spectra are measured and analyzed by AI to identify different amounts and types of

gut bacteria [34].

cost sensor that could eventually be used to develop an onsite sensing technology for

food and water [36].

Instead of using enzymes as the sensing molecule, one can use an “enzyme mimic”:

imprinted polymers. Imprinted polymers are polymers synthesized around a template,

which is then washed out, leaving a site specific for binding that template. In this exam-

ple, a sensor for mycotoxin was developed using an imprinted polymer [37]. Mycotoxin

is a toxin secreted from a fungus that attacks grain.

Mycotoxin fluoresces when irradiated with UV light, and a phone app was used to

determine the amount of fluorescence. The best detection limit achieved was 20 ng/mL.

Unfortunately, one needs to first prepare a grain extract to be able to use it, but this is a

big step toward a cheap, effective mycotoxin sensor for grain and food.

Besides optical sensing methods, gravimetric sensors [32], specifically the quartz-

crystal microbalance (QCM) [39], have been used for artificial tongues and noses. Elec-

trical sensors [32, 33], based on semiconductors, MOSFETs (Metal Oxide Semiconductor

Field Effect Transistors), conductive polymers, piezoelectricity, or carbon nanotubes, as

well as gas chromatography have also been used [23].

An example for a QCM sensors uses self-assembled N-Acetylglucosamine (GLcNAc)

monolayers [39]. GLcNAc is only part of the natural ligand for flu viruses, but even so

the sensor can identify three different serotypes of the flu virus (Figure 4.11).

Applications for artificial noses and tongues are quite varied. In the food indus-

try, it is used for process control, freshness determination, and authentication [23, 40].

Environmental and industrial monitoring is a common use for artificial noses, ranging

from local monitoring of pollutant gases such as NOx, SOx, and CO from car and power

plant exhausts or monitoring odors from landfills ([32] and references therein) to the