A novel double-codified nanolabel (DC-AuNP) based on gold nanoparticle (AuNP) modified with anti-human IgG peroxidase (HRP)-conjugated antibody is reported. It represents a simple assay that allows enhanced spectrophotometric and electrochemical detection of antigen human IgG as a model protein. The method takes advantage of two properties of the DC-AuNP label: first, the HRP label activity toward the OPD chromogen that can be related to the analyte concentration and measured spectrophotometrically; second, the intrinsic electrochemical properties of the gold nanoparticle labels that being proportional to the protein concentration can be directly quantified by stripping voltammetry. Beside these two main direct determinations of human IgG, a secondary indirect detection was also applicable to this system, exploiting the high molar absorptivity of gold colloids, by which, the color intensity of their solution was proportional to the concentration of the antigen used in the assay. Paramagnetic beads were used as supporting material to immobilize the sandwich-type immunocomplexes resulting in incubation and washing times shorter than those typically needed in classical ELISA tests by means of a rapid magnetic separation of the unbound components. A built-in magnet graphite-epoxy-composite electrode allowed a sensibly enhanced adsorption and electrochemical quantification of the specifically captured AuNPs. The used DC-AuNP label showed an excellent specificity/selectivity, as a matter of fact using a different antigen (goat IgG) a minimal nonspecific electrochemical or spectrophotometric signal was measured. The detection limits for this novel double-codified nanoparticle-based assay were 52 and 260 pg of human IgG/mL for the spectrophotometric (HRP-based) and electrochemical (AuNP-based) detections, respectively, much lower than those typically achieved by ELISA tests. The developed label and method is versatile, offers enhanced performances, and can be easily extended to other protein detection schemes as well as in DNA analysis.

The electrochemical properties of gold nanoparticles (AuNPs) have led to their widespread use as DNA labels. This fact has improved the design strategies for the electrochemical detection of DNA through hybridization event monitoring. The reported DNA hybridization detection modes are based on either AuNP detection after dissolving or the direct detection of the AuNP/DNA conjugates anchored onto the genosensor surface. Various enhancement strategies have been reported so as to improve the detection limit. Most are based on catalytic deposition of silver onto AuNP. Other strategies based on the use of AuNPs as carrier/amplifier of other labels will be also revised. The developed techniques are characterized by sensitivities and specificities that enable further applications of the developed DNA sensors in several fields.

A novel gold nanoparticle-based protocol for detection of DNA hybridization based on a magnetically trigged direct electrochemical detection of gold quantum dot tracers is described. It relies on binding target DNA (here called DNA1) with Au(67) quantum dot in a ratio 1:1, followed by a genomagnetic hybridization assay between Au(67)-DNA1 and complementary probe DNA (here called DNA2) marked paramagnetic beads. Differential pulse voltammetry is used for a direct voltammetric detection of resulting Au(67) quantum dot-DNA1/DNA2-paramagnetic bead conjugate on magnetic graphite-epoxy composite electrode. The characterization, optimization, and advantages of the direct electrochemical detection assay for target DNA are demonstrated. The two main highlights of presented assay are (1) the direct voltammetric detection of metal quantum dots obviates their chemical dissolution and (2) the Au(67) quantum dot-DNA1/DNA2-paramagnetic bead conjugate does not create the interconnected three-dimensional network of Au-DNA duplex-paramagnetic beads as previously developed nanoparticle DNA assays, pushing down the achievable detection limits.

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A novel, rapid, and sensitive protocol for the electrochemical detection of DNA hybridization that take the advantage of a magnetic separation/mixing process and the use of monomaleimido-gold nanoparticles of 1.4 nm diameter as label is presented. A sandwich-type assay is formed in this protocol by the capture probe DNA immobilized on the surface of magnetic beads and the double hybridization of the target (cystic fibrosis related DNA), first with the immobilized probe, and then with signaling probe DNA labeled with monomaleimido-gold nanoparticles. When the assay is completed, the final conjugate is transferred onto genomagnetic sensor surface (graphite epoxy composite electrode with a magnet inside) used as working electrode, and then the direct determination of gold nanoparticles by differential pulse voltammetry striping technique is carried out. This protocol is quite promising for numerous applications in different fields as clinical analysis, environmental control as well as other applications.

Different methods of synthesis for the production of electroactive nanocrystals (NCs) for use as labels in DNA sensing systems are presented. They are based on two general ways of controlling the formation and growth of the nanoparticles: (a) physical restriction of the volume available for the growth of the individual nanoparticles by using templates such as reverse micelles; (b) arrested precipitation that depends on exhaustion of one of the reactants. The water dispersed nanocrystals thus obtained are then characterized by optical or electrochemical techniques so as to evaluate the quality of the prepared NCs. A novel direct electrochemical stripping detection protocol that involves the use of a bismuth modified graphite epoxy composite electrode is developed and applied so as to quantify the CdS NCs. The electrochemical study revealed a linear dependency of the stripping current upon the concentration of CdS NCs with a detection limit of around 10(15) CdS NCs cm(-3). The obtained NCs are of great interest for future applications in electrochemical genosensors.

A new graphite-epoxy composite electrode (GECE) containing Bi(NO(3))(3) as a built-in bismuth precursor for simultaneous and individual anodic stripping analysis of heavy trace metals like lead and cadmium is reported. The developed Bi(NO(3))(3)-GECE is compatible with bismuth film electrodes reported previously including the composite electrodes (Bi-GECE) recently reported by our group. Bi(NO(3))(3)-GECE displays the ability for the detection of both individual and simultaneous determination of heavy trace metals and exhibits well defined, reproducible and sharp stripping signals. The sensitive response is combined with the minimal toxicity of Bi(NO(3))(3). This novel sensor would be an appropriate alternative tool to sensors using bismuth in solution during their utilization in environmental quality monitoring as well as other applications.