# Recent Advances in Electrochemical Immunosensors
## 3 Discussion
### Dendrimers
#### 3.6.1 Enzyme-Based Immunosensors  
[PERSON] et al. [164] reported detection of \(\alpha\)-synuclein (\(\alpha\)-SYN), a neuronal protein, based on a dual signal amplification strategy. AuNPs decorated with G4 PAMAM (polyamidoamine) were covalently bound on poly-o-aminobenzzoic acid electropolymerized on the electrode surface, onto which \(\alpha\)-SYN was adsorbed as capture antibodies. Then, \(\alpha\)-SYN/HRP/AuNPs were introduced as signaling antibodies. The electrocatalytic response upon oxidation of Thi (introduced in solution) was monitored by CV and gave a linear response between 20 pg mL\({}^{-1}\) and 200 ng mL\({}^{-1}\), with a LoD of 15 pg mL\({}^{-1}\) (Figure 32A).  
Figure 32: _Cont._  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Target** & **Probe** & **LoD** & **Method** & **Reference** \\ \hline PSA protein & Ab & 100 fg mL\({}^{-1}\) & Au/Fe\({}_{3}\)O\({}_{4}\)HRP/Fe/H\({}_{2}\)O\({}_{2}\) & [146] \\ CEA protein & Ab & 1.0 pg mL\({}^{-1}\) & AgNPs/HRP/H\({}_{2}\)O\({}_{2}\)/o-PD/CV & [147] \\ Ochratoxin A & Ab & 0.10 mg L\({}^{-1}\) & MBs/HRP/H\({}_{2}\)O\({}_{2}\)/HQ/DPV & [148] \\ ALVs-J & Ab & 150 TCLD\({}^{00}\) mL\({}^{-1}\) & 6 CD-Fe/Fe\({}_{3}\)O\({}_{4}\)/GOx & [149] \\ _E. coli_ & Ab & 1000 CFU mL\({}^{-1}\) & MBs/GOx/Glucose/EIS & [150] \\ Transferrin & Ab & 0.03 ng mL\({}^{-1}\) & MBs/HRP/H\({}_{2}\)O\({}_{2}\)/TMB & [151] \\ TGF-\(\beta\)1 & Ab & 10 pg mL\({}^{-1}\) & MBs/polyHRP/HQ/H\({}_{2}\)O\({}_{2}\) & [152] \\ CTC & Ab & \(2.2\times 10^{2}\) cells & AuNPs/HER & [153] \\ Aflatoxin B1 & Ab & 0.2 ng mL\({}^{-1}\) & Au/Fe\({}_{3}\)O\({}_{4}\) MBs/Catechol/DPV & [154] \\ _E. coli_ & Ab & 10 CFU mL\({}^{-1}\) & MBs/Nanoporous Al\({}_{2}\)O\({}_{3}\)/EIS & [155] \\ _E. coli_ & Ab & 300 CFU mL\({}^{-1}\) & AuNPs/HER & [156] \\ SCC-Ag & Ab & 15 pg mL\({}^{-1}\) & Pt/Fe\({}_{3}\)O\({}_{4}\) MBs/H\({}_{2}\)O\({}_{2}\) & [157] \\ Clenbutered & Ab & 0.2 ng mL\({}^{-1}\) & Au/Fe\({}_{3}\)O\({}_{4}\) MBs/Fe(CN)\({}_{6}\)\({}^{3-4-}\)/DPV & [158] \\ Digoxin & Ab & 50 pg mL\({}^{-1}\) & Au/Fe\({}_{3}\)O\({}_{4}\) MPs/AuCl\({}_{4}\)–/DPV & [159] \\ Apolipoprotein & Ab & 68 ng mL\({}^{-1}\) & IrO\({}_{2}\) NPs/Amperometry & [160] \\ Apolipoprotein & Ab & 20–80 pg mL\({}^{-1}\) & MBs/AuNPs/Amperometry & [161] \\ EGFR & Aptamer & 50 pg mL\({}^{-1}\) & MBs/AuNPs/ASV & [162] \\ Interferon-\(\gamma\) & Ab & 0.01 IU mL\({}^{-1}\) & MPs/AuNPs/CdSNPs/SWASV & [163] \\ \hline \hline \end{tabular}
\end{table}
Table 9: Figures of merit of selected immunosensors using magnetic nanoparticles.  
[PERSON] et al. [165] also described an electrochemical immunosensor based on an amine-terminated polyamidoamine (PAMAM) dendrimer for detection of CEA. Anti-CEA (as capture probe) and the mediator Thi were immobilized on AuNPs encapsulated in the dendrimers. In a sandwich format, signaling anti-CEA coupled to GOx+HRP-modified MWCNTs were used for transduction (Figure 32C). The detection range was between 10.0 pg mL\({}^{-1}\) and 50.0 ng mL\({}^{-1}\) with a LoD of ca. 4 pg mL\({}^{-1}\). At last, [PERSON] et al. [166] described a triple signal amplification strategy for immunostaining of PSA by modification of GC electrodes with GO/Chi onto which PSA antibody and Thi were covalently attached. Recognition was made through a sandwich-type immunoreaction between PSA, anti-PSA immobilized on the GO/Chi interface, and HRP-functionalized PSA aptamers immobilized on PAMAM/AuNPs. Using DPV, the LoD was 10 fg mL\({}^{-1}\) and the detection range between 0.1 pg mL\({}^{-1}\) and 90 ng mL\({}^{-1}\).