# Recent Advances in Electrochemical Immunosensors
## 3 Discussion
### Magnetic Nanoparticles  
As shown above, in terms of sensitivity, the main objective now is to increase the ratio between the active surface of the sensor and the volume of analyzed solution. This could be adressed by making highly porous materials; this could also be adressed by using a strategy where the probe molecules, attached on small magnetic NPs, are diffusing in solution for reaction. These magnetic nanoparticles, dispersed in the analytical solution are able to \"fish\" the analyte before to be magnetically collected on the working electrode for transduction. This has been reported in the literature whether coupled with enzymatic amplification, or not.  
Figure 26: _Cont._  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Target** & **Probe** & **LoD** & **Method** & **Reference** \\ \hline IgG & Ab & 0.02 mg mL\({}^{-1}\) & AuNPs/PPy/Fe(CN)\({}_{6}\)\({}^{3-/4-}\)/EIS & [116] \\ Cancer cells & Ab & \(4\times 10^{3}\) cells & AuNPs/CV & [117] \\ HbA1c protein & Peptide & 10 mg mL\({}^{-1}\) & AuNPs/Ru(NH\({}_{3}\))\({}^{2+/3+}\)/EIS & [118] \\ Dengue NSI protein & Ab & 0.5 mg mL\({}^{-1}\) & Fc-labelled Ab/EIS & [119] \\ Mycotoxins & Ab & 1 mg mL\({}^{-1}\) & AuNP/PPy/Fe(CN)\({}_{6}\)\({}^{3-/4-}\) & [120] \\ Amyloid beta 1–42 & Ab & 5 pg mL\({}^{-1}\) & AuNPs/Fe(CN)\({}_{6}\)\({}^{-3-/4-}\) & [121] \\ _P_/HRP2 & Ab & 70 mg L\({}^{-1}\) & PtNPs/MB/Hydrazine & [122] \\ _E. coli_ & Ab & 400 cells mL\({}^{-1}\) & MWCNT/PbS/SWASV & [123] \\ CA72-4 carbohydrate & Ab & 0.10 U mL\({}^{-1}\) & AuNPs/PANi/H\({}_{2}\)O\({}_{2}\) & [124] \\ Atrazine & Ab & 0.02 mg mL\({}^{-1}\) & Fe(CN)\({}_{6}\)\({}^{3-/4-}\)/DV & [125] \\ Cortisol & Ab & 0.4 mg L\({}^{-1}\) & ZnO nanorods/Fe(CN)\({}_{6}\)\({}^{3-/4-}\)/EIS & [126] \\ CEA protein & Ab & 0.1 pg mL\({}^{-1}\) & AuNPs/Ag enhancement/ASV & [127] \\ CEA protein & Ab & 8 U mL\({}^{-1}\) & AuNPs/Ag enhancement/ASV & [128] \\ CEA protein & Ab & 0.015 g mL\({}^{-1}\) & AuNPs/Fe(CN)\({}_{6}\)\({}^{3-/4-}\)/DPV & [129] \\ CEA protein & Ab & 3 fg mL\({}^{-1}\) & AuNPs/Fe(CN)\({}_{6}\)\({}^{3-/4-}\)/CV & [130] \\ CEA protein & Ab & 2 pg mL\({}^{-1}\) & PtNPs-Cd\({}^{2+}\)/DPV & [131] \\ AFP protein & Ab & 4 pg mL\({}^{-1}\) & Pd nanoplates/Fe(CN)\({}_{6}\)\({}^{3-/4-}\) & [132] \\ CEA protein & Ab & 0.02 ng mL\({}^{-1}\) & PAA NPs/Cd\({}^{2+}\)/SWV & [133] \\ CEA protein & Ab & 0.5 fg mL\({}^{-1}\) & AgNPs/THI/Fe(CN)\({}_{6}\)\({}^{3-/4-}\)/DPV & [134] \\ CEA protein & Ab & 0.1 pg mL\({}^{-1}\) & AuNPs/Fe(CN)\({}_{6}\)\({}^{3-/4-}\)/EIS & [135] \\ CEA protein & Ab & 10 pg mL\({}^{-1}\) & GR/THI/AUNPs & [136] \\ CEA protein & Ab & 7 pg mL\({}^{-1}\) & PANi-AuNPs/EIS/conductivity & [137] \\ CEA protein & Ab & 0.5 pg mL\({}^{-1}\) & AuNPs/Thi/MoS\({}_{2}\) & [138] \\ CEA protein & Ab & 8 pg mL\({}^{-1}\) & Ag/AuNPs/Ag\({}^{0}\)/Ag\({}_{2}\)O/CV & [139] \\ HSA protein & Ab & 1 ng mL\({}^{-1}\) & SiO\({}_{2}\)NPs/AuNPs oxidation/DPV & [140] \\ PSA protein & Ab & 15 pg mL\({}^{-1}\) & SiO\({}_{2}\)NPs/HQ/CV & [141] \\ PSA protein & Ab & 0.3 pg mL\({}^{-1}\) & Fc-PtNPs/H\({}_{2}\)O\({}_{2}\) & [142] \\ PSA protein & Ab & 0.03 pg mL\({}^{-1}\) & Cu\({}_{2}\)O@CeO\({}_{2}\)NPs/AuNPs/H\({}_{2}\)O\({}_{2}\) & [143] \\ PSA protein & Ab & 1 pg mL\({}^{-1}\) & AuNPs/Ag enhancement/LSV & [144] \\ PSA protein & Ab & 150 fg mL\({}^{-1}\) & Cu nanoclusters/ascorbic acid & [145] \\ \hline \hline \end{tabular}
\end{table}
Table 8: Figures of merit of selected non-enzymatic immunosensors using metal or metal oxide nanoparticles.