# Recent Advances in Electrochemical Immunosensors
## 3 Discussion
### Ionic Liquids  
We reviewed here in this section some recent advances in the use of ionic liquids in the construction of electrochemical immunosensors. As discussed above, the use of metal nanoparticles or graphene, or a combination of the two, were used as building materials to improve the sensing performances. However, water dispersability of these materials is low and they present a strong \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Target** & **Probe** & **LoD** & **Method** & **Reference** \\ \hline \(\alpha\)-Synuclein protein & Ab & 15 pg mL\({}^{-1}\) & PAMAM/AuNPs/HRP/Thi/CV & [164] \\ CEA protein & Ab & 4 pg mL\({}^{-1}\) & PAMAN/AuNPs/GOx-HRP/Thi & [165] \\ PSA protein & Ab & 10 fg mL\({}^{-1}\) & PAMAM/AuNPs/HRP & [166] \\ AFP protein & Ab & 0.025 pg mL\({}^{-1}\) & PAMAM/C-dots/AuNPs/Fe(CN)\({}_{6}\)\({}^{3-/4-}\) & [167] \\ AFP protein & Ab & 130 fg mL\({}^{-1}\) & PAMAM/AuNPs/Viologen & [168] \\ CA 125 protein & Ab & 5 mU mL\({}^{-1}\) & MBs/PAMAM/QDs/ CdS/ASV & [169] \\ IgG & Ab & 2 ng mL\({}^{-1}\) & anti-IgG/G\({}_{2}\)Fc/Fc & [170] \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Figures of merit of selected immunosenors using dendrimers. Figure 33: (**A**) Use of signaling antibodies coupled to dendrimers (PAMAN) containing metal sulfides, and (**B**) subsequent electroreduction by ASV for detection. This method allows detecting several antibody-antigen complexes. Reprinted from [169], Copyright 2013, with permission from Elsevier. tendency to agglomerate into multilayer graphite of bundles of NPs through \(\pi\)-\(\pi\) stacking or Van der Waals interaction, which limits their application. It was shown that ionic liquid, used for surface functionalization of such NPs, could be a solution. In 2013, [PERSON] et al. [171] reported ionic liquid-functionalized GR sheets loaded with AuNPs onto which antibodies were immobilized, for detection of CEA. Using DPV and Fe(CN)\({}_{6}\)\({}^{3-/4-}\) as diffusing redox probe, this immunosensor showed a linear detection range from 1 fg mL\({}^{-1}\) to 100 ng mL\({}^{-1}\), and a LoD of 0.1 fg mL\({}^{-1}\). [PERSON] and [PERSON] [172] described an IL-functionalized RGO material for CEA and AFP detection. Due to the modification with 1-aminopropyl-3-methylimidazolium chloride, GO sheets were easily dispersed in aqueous solution to form a homogeneous colloidal suspension. Signaling antibodies were coupled to Prussian blue NPs and CdNPs and used in a sandwich immunoassay (Figure 34). Using DPV, the linear ranges were from 0.01 to 100 ng mL\({}^{-1}\) for both CEA and AFP. The LoD was 10 pg mL\({}^{-1}\) for CEA and 6 pg mL\({}^{-1}\) for AFP. [PERSON] et al. [173] reported an immunosensor for microcystin-LR, a family of water contaminant composed on a stable heptapeptide produced mainly by common cyanobacteria. GC electrodes were modified with GO and AuNPs, and 2,5-di-(2-thienyl)-1-pyrrole-1-(\(p\)-benzoic acid) was grafted to immobilize the microcystin-LR antibodies. The IL (1-isobutyl-3-methylimidazolium bis(trifluor-methanesulfonyl)imide) was then dropped on the electrode surface and finally microcystin-LR antibody was covalently bound to the conducting polymer film. Electrochemical detection was made with DPV in the range \(10^{-16}\)-\(8\times 10^{-15}\) M using Fe(CN)\({}_{6}\)\({}^{3-/4-}\) added in solution, and the authors reported an extremelly low LoD of \(4\times 10^{-17}\) M (i.e., \(4\times 10^{-17}\) g mL\({}^{-1}\)). This article was very similar to another one of the same authors published one year before [174], reporting an immunosensor for aflatoxin B\({}_{1}\), for which the LoD was of 1 fM and the linear range from 3.2 fM to 0.32 pM, measuring the charge transfer resistance by EIS. [PERSON] el al. [175] reported in 2016 an immunoassay for detection of hCG. First, PtNPs were immobilized on a composite layer of graphene, chitosan and an ionic liquid (1-methyl-3-octyl imidazolium tetrafluoroborate). The amine groups of the antibody were covalently attached to PtNPs, whereas rutin was used in solution as redox probe.