Nanomaterial-based biosensors have become one of the major topics in the field of diagnostics. With the growing demand on devices with improved sensitivity and selectivity, rapid response time, and low cost, four categories of nanomaterials have become popular in biosensor research: gold nanoparticles, graphene, carbon nanotubes, and photonic crystals. The ongoing research has brought new designs of biosensors based on nanomaterials, which have greatly improved the potential of field-deployable microfabricated devices. This review describes the recent technologies employing the aforementioned nanomaterials for electrochemical detection of biomolecules, including glucose, DNA, protein, toxins, and so on. We envisage that miniaturized lab-on-a-chip devices employing these nanomaterials will soon be an essential part of our daily life.

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Legionellosis is a severe respiratory illness caused by the inhalation of aerosolized water droplets contaminated with the opportunistic pathogen Legionella pneumophila . The ability of L. pneumophila to produce biofilms has been associated with its capacity to colonize and persist in human-made water reservoirs and distribution systems, which are the source of legionellosis outbreaks. Nevertheless, the factors that mediate L. pneumophila biofilm formation are largely unknown. In previous studies we reported that the adhesin Legionella collagen-like protein (Lcl), is required for auto-aggregation, attachment to multiple surfaces and the formation of biofilms. Lcl structure contains three distinguishable regions: An N-terminal region with a predicted signal sequence, a central region containing tandem collagen-like repeats (R-domain) and a C-terminal region (C-domain) with no significant homology to other known proteins. Lcl R-domain encodes tandem repeats of the collagenous tripeptide Gly-Xaa-Yaa (GXY), a motif that is key for the molecular organization of mammalian collagen and mediates the binding of collagenous proteins to different cellular and environmental ligands. Interestingly, Lcl is polymorphic in the number of GXY tandem repeats. In this study, we combined diverse biochemical, genetic, and cellular approaches to determine the role of Lcl domains and GXY repeats polymorphisms on the structural and functional properties of Lcl, as well as on bacterial attachment, aggregation and biofilm formation. Our results indicate that the R-domain is key for assembling Lcl collagenous triple-helices and has a more preponderate role over the C-domain in Lcl adhesin binding properties. We show that Lcl molecules oligomerize to form large supramolecular complexes to which both, R and C-domains are required. Furthermore, we found that the number of GXY tandem repeats encoded in Lcl R-domain correlates positively with the binding capabilities of Lcl and with the attachment and biofilm production capacity of L. pneumophila strains. Accordingly, the number of GXY tandem repeats in Lcl influences the clinical prevalence of L. pneumophila strains. Therefore, the number of Lcl tandem repeats could be considered as a potential predictor for virulence in L. pneumophila isolates.

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We present a proof of concept study for electrochemical detection of the metal-binding site of α-synuclein (α-syn). Parkinson’s disease (PD) is associated with the aggregation and misfolding of α-syn in dopaminergic neurons. Because copper homeostasis is deregulated in PD, it is of great significance to study the metal-binding site of wild-type α-syn (48–53, VVHGVA) and its pathological mutants (H50Q and G51D). Cyclic voltammetry and electrochemical impedance spectroscopy were used to monitor the formation of a peptide-PEG mixed layer on gold surfaces. Differential pulse voltammetry was used to detect and evaluate the interaction of copper­(II) with the peptide layer. X-ray photoelectron spectroscopy was used to characterize the formation and attachment of the peptide layer on gold surfaces. Isothermal titration calorimetry was also utilized to evaluate the binding characteristics of the peptides with copper­(II) ions. Our results indicated that the effect of a single amino acid mutation on the peptides drastically influenced their ability to interact with copper­(II) ions. These results demonstrated that our electrochemical approach provided a rapid and cost-effective platform to study the strong interaction between α-syn and copper­(II), which is implicated as one of the factors inducing structural changes in α-syn toward the progression of PD.

The adhesin Legionella collagen-like (Lcl) protein can bind to extracellular matrix components and mediate the binding of Legionella pneumophila to host cells. In this study, electrochemical impedance spectroscopy (EIS) and surface plasmon resonance (SPR)-based biosensors were employed to characterize these interactions between glycosaminoglycans (GAGs) and the adhesin Lcl protein. Fucoidan displayed a high affinity (KD 18 nM) for Lcl protein. Chondroitin sulfate A and dermatan sulfate differ in the position of a carboxyl group replacing D-glucuronate with D-iduronate. Our results indicated that the presence of D-iduronate in dermatan sulfate strongly hindered its interaction with Lcl. These biophysical studies provided valuable information in our understanding of adhesin-ligand interactions related to Legionella pneumophila infections.

In this proof-of-concept study, a novel nanocomposite of the thiolated polyaniline (tPANI), multi-walled carbon nanotubes (MWCNTs) and gold–platinum core-shell nanoparticles (Au@Pt) (tPANI-Au@Pt-MWCNT) was synthesized and utilized to modify a glassy carbon electrode (GCE) for simultaneous voltammetric determination of six over-the-counter (OTC) drug molecules: ascorbic acid (AA), levodopa (LD), acetaminophen (AC), diclofenac (DI), acetylsalicylic acid (AS) and caffeine (CA). The nanocomposite (tPANI-Au@Pt-MWCNT) was characterized with transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Using the sensor (GCE-tPANI-Au@Pt-MWCNT) in connection with differential pulse voltammetry (DPV), the calibration plots were determined to be linear up to 570.0, 60.0, 60.0, 115.0, 375.0 and 520.0 µM with limit of detection (LOD) of 1.5, 0.25, 0.15, 0.2, 2.0, and 5.0 µM for AA, LD, AC, DI, AS and CA, respectively. The nanocomposite-modified sensor was successfully used for the determination of these redox-active compounds in commercially available OTC products such as energy drinks, cream and tablets with good recovery yields ranging from 95.48 ± 0.53 to 104.1 ± 1.63%. We envisage that the electrochemical sensor provides a promising platform for future applications towards the detection of redox-active drug molecules in pharmaceutical quality control studies and forensic investigations.