# Recent Advances in Electrochemical Immunosensors
## 1 Introduction  
The field of electrochemical immunosensors is very rich and dynamic. To give a general but concise overview of the current state-of-the-art, we have focused this review only on the major publications of the last five years (2012-2017), i.e., those which could justify of several tens of citations to date for the oldest (2012-2014), and at least some for the most recent ones.  
Of course, several reviews are already available on this topic, but these do not cover the period covered by this review, or are less general. A relatively brief review published by [PERSON] et al. in 2012 [1], presented a guide to all researchers interested in entering the electrochemical immunosensor domain, by reviewing the literature over the 2008-2012 period and focusing particularly on practical aspects. Another review, published by [PERSON] et al., also in 2012 [2], focused on new trends in signal amplification in enzyme-based immunosensors (combination of enzymatic reactions, multienzyme labels, use of magnetic beads...). The other reviews available since 2012 are more specialized, focusing on materials, transductions or applications. Concerning materials and transductions, [PERSON] et al. [3] dealt in 2013 with mesoporous silica materials for use in electrochemical immunosensing. [PERSON] et al. [4] published also in 2013 a review dealing specially with sandwich-type immunosensors exploiting nanostructured materials. More recently, in 2016, [PERSON] et al. [5] reviewed more particularly screen-printed electrodes modified by nanomaterials such as carbon nanotubes, graphene, metallic nanoparticles (gold, silver and magnetic nanoparticles) coupled with enzymes or antibodies and showed how it could improve performances. They gave, as perspective, some recent examples ofpaper-based, wearable or smartphone-driven devices. Concerning reviews which focus on precise applications rather than on materials, [PERSON] et al. [6] dealt in 2013 with generalities on point-of-care diagnostics for early detection of diseases. They also reviewed attempts to propose integrated systems, several being commercially available today. [PERSON] et al. [7] did the same in 2015 for early clinical diagnostics of cancer and cardiac diseases. More focused on one given application, or specific for a class of biomarkers or pollutants, [PERSON] et al. [8] reviewed in 2012 the most recent advances at that time in electrochemical immunosensors for detection of cancer protein biomarkers, with strategies to increase densities of capture molecules and sensitivities. On their side, in 2013, [PERSON] et al. [9] reviewed electrochemical affinity biosensors for detection of mycotoxins in food. This review focused on affinity probes in general but antibodies, including recombinant antibodies, are addressed. Also in 2013, [PERSON] et al. [10] reviewed electrochemical immunosensors for precise applications in breast and ovarian cancer. Finally, [PERSON] et al. [11] reviewed very recently (2017) electrochemical bioaffinity sensors for salivary biomarkers.  
This review presents the most recent advances in electrochemical immunodetection using enzymes and redox reactions for transduction and amplification, or enzyme-less strategies using innovative inorganic catalysts. We will focus first on classical electrode substrates, then move to carbon-based nanostructured ones including carbon nanotubes, graphene and other carbon materials. We will follow with the use of metal or metal-oxide nanoparticles, magnetic nanoparticles, dendrimers and, finally, we cite a few works using ionic liquids.