Electrochemical immunosensors are affinity-based biosensors characterized by several useful features such as specificity, miniaturizability, low cost and simplicity, making them very interesting for many applications in several scientific fields. One of the significant issues in the design of electrochemical immunosensors is to increase the system’s sensitivity. Different strategies have been developed, one of the most common is the use of nanostructured materials as electrode materials, nanocarriers, electroactive or electrocatalytic nanotracers because of their abilities in signal amplification and biocompatibility. In this review, we will consider some of the most used nanostructures employed in the development of electrochemical immunosensors (e.g., metallic nanoparticles, graphene, carbon nanotubes) and many other still uncommon nanomaterials. Furthermore, their diagnostic applications in the last decade will be discussed, referring to two relevant issues of present-day: the detection of tumor markers and viruses.

We report a new sensitive label-free electrochemical immunosensor to detect Vitamin D₃ (25-OHD₃) in untreated serum samples. To this aim, a graphite screen printed electrode (SPE) was modified using cysteamine (CYM) functionalized core-shell magnetic nanoparticles (Au@MNPs) then, the 25-OHD₃ antibody (AbD) was immobilized via glutaraldehyde crosslinking. The several steps involved in the immunosensor development and 25-OHD₃ analysis were monitored by using differential pulse voltammetry (DPV). The developed immunosensor showed a LOD of 2.4 ng mL^-1 and a linear range between 7.4 and 70 ng mL^-1. The effectiveness of the immunosensor in human serum analysis was assessed by comparing the results obtained with the chemiluminescence-immunoassay (CLIA) reference method. The high sensitivity and excellent agreement with the reference method suggest its potential use as a POCT to monitor hypovitaminosis 25-OHD levels.

Nanoparticle‐based electrochemical immunosensors are fascinating and promising screening systems that rely on the affinity binding between antibodies and antigens, allowing the specific detection of diverse types of targets (e. g., proteins, hormones, antibodies). The employment of nanoparticles in the realization of such devices dramatically improves the selectivity, sensitivity, and the transducer surface area for effectively immobilizing the bioreceptor or target molecules. During the last years, the nanoparticles design and fabrication was mainly focused on taking advantage from synergistic effects due to the coupling of different materials. In this review, we summarize the very recent advancements in this regard, with specific emphasis to nanoparticle syntheses procedures, antibody oriented immobilization strategies and transduction techniques. Moreover, the last trends and applications have been extensively discussed along with the remaining challenges and future perspectives.

Calix[n]arenes, as the ‘third-generation’ host molecules, are cyclic oligomer, featuring a unique three-dimensional structure with a hydrophobic cavity, allowing the interaction with many size-matched guest molecules, and a surface which can be functionalised at both the upper and lower rims with several functional groups to tailor the recognition properties towards a specific class of analytes for various applications. In the last two decades, due to their configuration, unique molecule recognition function and aggregation properties, calixarenes and their derivatives have attracted considerable attention as a new versatile scaffold for highly sensitive detection and site-oriented immobilisation in biosensor development. In this review, the development of sensors featuring calixarene-based transducers tuned for binding many analytes, ranging from simple (i.e., amino acids and neurotransmitters) to complex (i.e., enzymes and antibodies) organic molecules, was described. The rational design, the synthetic strategies fine-tuned to prepare these complex structures and their grafting in surface modification were included. GRAPHICAL ABSTRACT

This work aimed to develop an easy-to-use smartphone-based electrochemical biosensor to quickly assess a coffee blend’s total polyphenols (Phs) content at the industrial and individual levels. The device is based on a commercial carbon-based screen-printed electrode (SPE) modified with multi-walled carbon nanotubes (CNTs) and gold nanoparticles (GNPs). At the same time, the biological recognition element, Laccase from Trametes versicolor, TvLac, was immobilized on the sensor surface by using glutaraldehyde (GA) as a cross-linking agent. The platform was electrochemically characterized to ascertain the influence of the SPE surface modification on its performance. The working electrode (WE) surface morphology characterization was obtained by scanning electron microscopy (SEM) and Fourier-transform infrared (FT-IR) imaging. All the measurements were carried out with a micro-potentiostat, the Sensit Smart by PalmSens, connected to a smartphone. The developed biosensor provided a sensitivity of 0.12 μA/μM, a linear response ranging from 5 to 70 μM, and a lower detection limit (LOD) of 2.99 μM. Afterward, the biosensor was tested for quantifying the total Phs content in coffee blends, evaluating the influence of both the variety and the roasting degree. The smartphone-based electrochemical biosensor’s performance was validated through the Folin–Ciocâlteu standard method.