## 2 Impedance Spectroscopy
### Scopes of Application
#### 2.1.1 IS in Human Health Safety Due to Water Sources Contamination
[PERSON] and [PERSON] [46] used EIS on two aptasensors (a platinum counter electrode and Ag/AgCl or KCl reference electrodes were combined for the evaluation of the two under test working aptasensor electrodes, for frequencies between 0.01 Hz and 100 kHz, with an AC voltage of amplitude 10 mV), one based on a carbon paste electrode with oleic acid and the other based on a magnetic bar carbon paste electrode containing Fe\({}_{3}\)O\({}_{4}\) magnetic nanoparticles and oleic acid (following the modification of electrode surfaces using an anti-TET, tetracycline approach), to perform label-free detection of tetracycline (an oral antibiotic). When used for assessing tetracycline content in pharmaceutical formulations, serum samples, and food products (milk and honey), the sensors' detection limits were 1.0 \(\times\) 10\({}^{-12}\) to 1.0 \(\times\) 10\({}^{-7}\) M and 3.0 \(\times\) 10\({}^{-13}\) M, respectively. [PERSON] et al. [47] fabricated an EIS-operated sensor (for testing it, they used a standard three-electrode system, including a gold working electrode, a Pt wire counter electrode, and an Ag/AgCl-saturated KCl as reference electrode; data were recorded within the frequency range of 0.01 Hz-100 kHz with an AC voltage amplitude of 5 mV) based on nanocomposites of mC with SnO\({}_{\text{x}}\) and TiO\({}_{\text{2}}\) nanocrystals, and they used it to evaluate the presence of tobramycin (an aminoglycoso antibiotic) in urine and serum samples, and the presence of kanamycin, oxytetracycline, and doxycycline (all also antibiotics); the sensor displayed a detection limit of 0.01 nM. [PERSON] and colleagues [48] evaluated Bisphenol A (a xenoestrogen with an estrogen mimicking effect, not produced by the human body, widely used as a precursor in the plastics industry) utilizing a labelled EIS-stimulated aptasensor (the cell was composed of a rod of GNPs and functionalized carbon nanotubes, GNPs/PB/CNTs-COOH, a working electrode, an Ag/AgCl reference electrode, and a Pt wire auxiliary electrode; testing was made using alternating voltage potential of 10 mV with a 0.190 V DC potential, in the frequency range from 0.1 Hz to 10 KHz). The determination of progesterone (a hormone that supports menstruation and maintains pregnancy, and of which low levels can cause complications) in water and other clinical samples was performed using single-stranded ssDNA aptamers that possessed high binding affinity with progesterone P4. [PERSON] et al. [49] assessed raoxifene interfacial properties (a selective estrogen receptor modulator that is used to prevent and treat osteoporosis and reduce the risk of invasive breast cancer), utilizing three sensing electrode materials and EIS; a bare screen-printed carbon electrode, a graphene oxide/glassy carbon electrode, and a neodymium sesquioxide nanoparticles electrode (Nd\({}_{2}\)O\({}_{5}\) NPs@GO/GCE). The results obtained showed that the charge transfer resistance of the neodymium sesquioxide nanoparticles electrode was much lower than that of the other two. In a work by [PERSON] and co-authors [50], oxytetracycline (a tetracycline class of antibiotics, a subset of antimicrobials included in an essential class of pharmaceutically active materials) was tested for label-free detection in milk samples. A mixture of iron oxide and mesoporous carbon (Fe\({}_{3}\)O\({}_{4}\)@mC), together with nanocomposites made from Fe(II)-based metal-organic frameworks (525-MOF), was calcined at different temperatures and used as sensing material.