Nanotechnology has recently become one of the most exciting forefront fields in analytical chemistry. A wide variety of nanoscale materials of different sizes, shapes and composltlons at the 1-100 nm scale, are now available. Metal and polymeric nanoparticles were applied in this work for desigining novel sensing systems, enhancing the perfomance of bioanalytical assays and improving the visualisation of biointeractions ocurring on sensing surfaces. A novel nanoparticulate formulation of the condructing polymer polyaniline (PANI) was applied foi the development of a chemlcal sensor device capable of detecting both ascorbic acid and hydrogen peroxide. The "nanoPANI"-modified electrode showed enhanced electrocatalysls over tradltlonal bulk PAN1 films for hydrogen peroxide. lnkjet printing deposition of this highly processable nanomatcrial onto screen-printed electrodes was also demonstrated for simple and rapld sensor device production. An enzyme-channelling system for the detection of glucose was optmused with HRP and GOX enzymes and applied to an mununosensor platform to report the immunological interaction between biotin and avidin. After the evaluation of the efficrency of this system, a slgrd enhancement approach was then attempted by means of AuNPs as multi-enzyme carriers. Charactensahon of the enzyme-NP conjugates was also performed by spectrophotometzlc and electrochemical analyses. AuNPs were also used to develop a multi-detection lmmunoassay system A sandwch-type platform was prepared using stueptavidln-modified paramagnetic beads as supporting material, blotinylated anti-human IgG as primary antibodys pecific to human IgG and Au-labelled anti-human-HRP as secondary antibody Using AuNPs as labels offered the posslbllity of the spectrophotometnc analysis based on elther AuNP absorphon or HRP enzymatic activity aid also electrochemcal analysls based on the drrect detection of AuNPs Both the opt~cal and the electrochemical analysis of a human IgCr model proteln resulted in enhanced senwfivity when compared to the classical ELISA tests where HRP-labelled antibodies are used. Silver-enhanced AuNPs were finally used to visualize an immunomteraction occurring at an electrode surface by means of SEM A AuNP-labelled anti-goat antibody was used as the target proteln to interact with two imunosensor platforms prepared immobilising anti-atrazine (single chain) and mtr-biotin antlbohes onto PAM-modified electrodes Comparing the images of the immunosensor surfaces with those of different control surfaces, it was possible to gain an appreciation of the extent and distribuhon of the munological interaction and the level of non-specific binding occurring at the electrode. In general, the application of these nanoparticles resulted in many advantages for the senslng systems investigated m this work These Include the observabon of enhanced electrocatalytic pheilomena wth benefits in chemical and biosensing, in improved analytical performance of classical senslng platforms where metal NPs were used as electrical tracers, as well as the application of metal NPs to assist in the detailed physical charactensation of immunosensing systems.