## 2 Impedance Spectroscopy
### Scopes of Application
#### 2.1.1 IS in Human Health Safety Due to Water Sources Contamination  
Food and water safety have recently become universal concerns [31; 32; 33; 34; 35]; consequently, there is a significant demand for methods capable of detecting water and food contaminants. For instance, in the case of water (the most crucial source for human existence and development), due to the evolution of human life the widespread use of chemicals came about and their resultant innumerable contaminants threaten aquatic systems (heavy metals, sulphates, phosphates, dyes, and pesticides, to mention some). If we take into consideration heavy metals (like As, Cd, Cr, Pb, and Hg, which have been reported to be very toxic), they are non-degradable and widely used in industrial, domestic, and agricultural applications; so, once food production became water-dependent, food safety became a significant issue and, consequently, the potential influence on public health of water pollution is extremely concerning. Dyes are also significant water pollutants; they can color substantial volumes of water, even if discharged as traces. The textile industry is one of the highest volume contributors, discharging significant amounts of polluted waste by dyes with various chemical structures. Dyes usage and their consequent release into the water directly affect aquatic beings and, indirectly, human health; the impact of these agents includes carcinogenicity and poisoning [36; 37]. As mentioned, the discharge of heavy metals, HMs, into the water via industrial activities, among other sources, significantly influences the environment and human health; their toxicity, degradation rate, accumulation, uptake, and bioavailability need to be evaluated. In the research carried out by [PERSON] et al. [38], a bi-enzymatic biosensor (_Arthospira platensis_ cells were immobilized on gold-interdigitated structures) was developed that inhibited phosphatase and esterase activities by heavy metals and pesticides, respectively, consequently avoiding their liberation in wastewaters. When they assessed the sensor operation by Electrical Impedance Spectroscopy, EleIS, they were able to determine Hg\({}^{2+}\) and Cd\({}^{2+}\) species, as well as parathion, paraoxon, and triazine pesticides, alone or in a mixture containing the heavy metals (and for the four-points measurement configuration, performed in the frequency range of 100 mHz to 100 kHz at room temperature). Trying to prevent the release of some heavy metals into wastewater, [PERSON] and his co-workers [39] fabricated a three-electrode sensor configuration printed on a polyethylene terephthalate film; using Electrochemical Impedance Spectroscopy, EIS, they applied this sensor to the impedimetric determination of Pb\({}^{2+}\) and Cd\({}^{2+}\) species in water samples at the nanomolar level (measurements were made while applying a voltage of 1 V and with operating frequencies in the range of 1 Hz to 100 kHz). EIS, applied in the frequency range of 1 mHz to 1 MHz, was also the way [PERSON] and colleagues [40] evaluated an electrochemical DNA biosensor made of cuprous oxide and nanochitosan microspheres, for Hg\({}^{2+}\) detection in river water (which included an Au electrode, a Pt-slide auxiliary electrode, and an Ag/AgCl reference electrode); the measured detection limit was of 0.15 nM. Examples of IS usage for exploring food contamination situations are likewise found in the literature. For instance, [PERSON] et al.