# New Generation of Electrochemical Sensors Based on Multi-Walled Carbon Nanotubes
## 4 Overview of MWCNT Applications in Electrochemical Sensors
[39] fabricated a non-enzymatic glucose sensor using a hybrid film (composed by \(f\)-MWCNT and highly monodisperse nickel nanoparticles) immobilized on GCE, which was able to determine this target in human blood serum samples by amperometry, with sensitivity (LOD = 0.021 umol L\({}^{-1}\)) and stability similar to one of commercial enzymatic biosensors. The results also support the positive synergistic effects that are observed when different nanomaterials are associated into the same matrix, enhancing the capacity and versatility of the electrochemical sensors. Purine bases are also crucial biomolecules to the immune function and abnormal changes causes serious disorders, such as cancer, epilepsy, lupus erythematosus, renal calculi, and cardiovascular alterations. [PERSON] et al. [40] prepared a nanocomposite by mixing  
Figure 5: (**a**) Schematic representation of the layer-by-layer and (**b**) supramolecular interaction between chitosan and multi-walled carbon nanotubes (MWCNT) for 1-bilayer film (adapted by permission from Reference [32]). MWCNT and copper-nickel hybrid nanoparticles (Cu@Ni-NP), which was deposited onto a GCE surface, with the goal of monitoring adenine and guanine in ds-DNA from mice brain tissues. Using DPV under the optimized conditions, the Cu@Ni-NP/MWCNT/GCE sensor achieved a LOD of 0.17 mol L\({}^{-1}\) and 0.33 mol L\({}^{-1}\) for guanine and adenine, respectively, attesting to its potential to quantify purine bases in complex samples. Likewise, sensors for point-of-care detection of DNA damage in medical diagnostics are also on the rise. [PERSON] and [PERSON] [41] investigated the performance of _f_-MWCNT (functionalization with oxygen-containing groups to improve the immobilization and stability of the bioelement) as an additive in electrochemical DNA sequence differentiation ability. The electroanalytical signal achieved by DPV was highly selective and modulated between the probe (5\({}^{\prime}\)-GTG TTG TCT CCT AGG TTG GCT CTG-3\({}^{\prime}\); 24-base fraction of the p53 gene, used as a marker for breast cancer) and its complementary sequence (5\({}^{\prime}\)-CAG AGC CAA CCT AGG AGA CAA CAC-3\({}^{\prime}\)). The detection capacity (LOD = 141.2 pmol L\({}^{-1}\)) was more than two orders better than the previously reported for graphene functionalized (_f_-Grf) based sensors, even in the presence of single (5\({}^{\prime}\)-CAG AGC CAA CCT CGG AGA CAA CAC-3\({}^{\prime}\)) and all-base mismatched pairs (5\({}^{\prime}\)-ATA TCG ACC TTG GCC GAG ACG GTG-3\({}^{\prime}\)). Great effort has also been directed towards the development of electrochemical devices capable of early detection of immune deficiency diseases, such as acquired immune deficiency syndrome (AIDS) caused by the HIV-retrovirus. [PERSON] et al. [42] proposed a device composed by a GCE modified with MWCNT and molecularly imprinted polymers (MIPs) based on CTS for the determination of HIV-p24 protein in real human serum samples (Figure 6). Using DPV and the developed sensor (HIV-p24/CTS/MWCNT/GCE), a low limit of detection (0.083 pg cm\({}^{-3}\)), good selectivity, repeatability, reproducibility, stability, and accuracy were reached for the proposed electroanalysis; validation was performed by comparative studies with enzyme-linked immunosorbent assay (ELISA). The outstanding ability of MWCNT-based electrochemical sensors to simulate redox reactions that occur in vivo has also been demonstrated with the electroanalysis of hemoglobin [43], amino acids [44], cholesterol [45], bilirubin [46], neurotransmitters, and related compounds [47; 48; 49], and even microorganisms [50], in mammalian fluid samples, achieving great results and contributing to the early diagnosis and treatment of several related diseases. The occurrence of pesticides in foodstuffs, natural water, soils, among other matrices of environmental relevance, constitute a worldwide concern. [PERSON] et al.