The first scope of the present thesis has been focused on the synthesis of new nanosorbents and their application in solid-phase microextraction of DNA and peptides. The other scope of the thesis was developing new optical apatasensors base on synthesized carbon quantum dots for determination of adenosine. In the first study, a zirconia magnetic nanocomposite was prepared by a co-precipitation method in one step. The synthesized nanocomposite was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and dynamic light scattering. The nanocomposite was applied for the adsorption/desorption of DNA. Experimental parameters controlling adsorption/desorption efficiency were optimized. The nanocomposite provided the adsorption capacity of 53.5 mg g -1 for DNA. The adsorption and desorption efficiency of the sorbent were found to be greater than 98 and 81%, respectively. The zirconia magnetic nanocomposite was used for the purification of plasmid DNA from Escherichia coli cell culture. In the second study, two hydrazide functionalized magnetic nanostructure sorbents base on aminosilane and chitosane were developed for the selective extraction of peptides with N-terminal serine and threonine. The synthesized sorbents characterization was performed by scanning electron microscopy and Fourier transform infrared. The studied peptides were labeled by oxidation of the hydroxyl group in 1,2-amino alcohol structure. The aldehyde-form peptides were immobilized on the surface of the sorbent through the hydrazide group. The formed hydrazone binds were broken by hydroxylamine reagent. The release oximated peptides were determined by HPLC-UV. The effect of extraction time, elution time and elution volume on extraction performance were studied. Extraction and desorption processes were performed in 6-8 h. The both sorbents showed excellent selectivity in extracting peptides with N-terminal serine and threonine in the presence of a peptide with non-N-terminal serine and threonine. The third study described a new optical aptasensor for determination of adenosine (AD) in human urine samples based on fluorescence resonance energy transfer between carbon quantom dots (CQDs) as a donor and a nanocomposite of silver nanoparticles and graphene oxide as quencher. In this work, a green path was introduced to synthesize CQDs with the high quantum yield as 47%, using corn gluten. An amino-modified aptamer was covalently joined to CQDs. This probe detected AD specifically and sensitively in a linear range from 12.5 to 271 nmol L -1 with a detection limit of 5 nmol L -1 . Moreover, the probe showed very good potential for determination of AD in urine samples of lung cancer patients. In the final work, two new simple aptasensor base on fluorescence and absorbance spectrometry for the determination of AD in human urine samples were described. The fluorometric sensor proposed a mixture of new CQDs as fluorescents, silver nanoparticles (Ag) as quencher of CQDs fluorescence and anti-AD aptamer as recognition probe. The second sensor only contained Ag as colorimetric elements and aptamer. The detection of AD for the both sensors was based on the dispersion and aggregation degree of Ag in the presence of salt. The detection limit was obtained 21 and 13 nmol L -1 by absorbance and fluorometric sensors, respectively. The method had high selectivity toward AD in the presence of other interferences.