[pt] Recentemente, os nanocristais semicondutores, também conhecidos como pontos quânticos, tornaram-se muito atrativos em abordagens de detecção por fotoluminescência devido as suas propriedades ópticas peculiares, tais como fluorescência intensa e com perfil estreito, comprimento de onda máximo ajustável através do controle do tamanho das partículas e maior fotoestabilidade em comparação com os corantes orgânicos convencionais. As nanopartículas sintetizadas foram avaliadas como sondas fotoluminescentes (na forma de dispersão aquosa) para a determinação de captopril, histamina, canamicina e tiroxina (analitos não fotoluminescentes na temperatura ambiente) evitando o uso de procedimentos complexos de derivatização química e permitindo quantificações de forma simples e com sensibilidade. Nanopartículas de CdTe modificadas com o ácido tioglicólico (TGA) e com o ácido 2-mercaptopropiônico (2MPA) e também nanopartículas de ZnS modificadas com L-cisteína foram sintetizadas pela abordagem em fase aquosa coloidal. Estas foram caracterizadas usando métodos microscópicos e espectroscópicos adequados. A fotoluminescência da nanopartícula 2MPA-CdTe foi consideravelmente mais intensa quando na presença de captropil. Sob condições ótimas, o modelo de calibração (isoterma de ligação de Langmuir) foi linear até 4,8 x 10-4 mol L-1 com constante de equilíbrio de ligação de 3,2 x 104 L mol-1 e limite de detecção (LOD) de 6,2 x 10-6 mol L-1 (1,3 (micro)g mL-1). Aplicações em soro sanguíneo humano fortificado com captropil e em formulações farmacêuticas foram demonstradas. A fotoluminescência das nanopartículas de TGA-CdTe foi reduzida (supressão) após adição de diferentes concentrações de histamina seguindo o modelo de Stern- Volmer. A resposta linear cobriu uma faixa de concentração até 5,7 x 10-4 mol L-1, com LOD de 9,6 x 10-6 mol L-1 (1,1 (micro)g mL-1). A abordagem proposta foi utilizada para determinação de histamina em carne de atum. Já a presença de aminoglicosídeos aumentou a fluorescência das nanopartículas de TGA-CdTe (seguindo o modelo da isoterma da adsorção de Langmuir). A kanamicina foi o aminoglicosídeo escolhido para estudar o efeito do aumento da intensidade da fotoluminescência das nanopartículas de TGA-CdTe disperso em solução aquosa. A faixa linear estendeu-se até 8,2 x 10-7 mol L-1 com LOD de 2,5 x 10-8 mol L-1 (14,2 ng mL-1). As constantes de ligação entre diversos aminoglicosídeos e TGACdTe foram calculadas e indicou que existe uma relação entre o número de grupos amino primários disponíveis e o aumento da luminescência. Essa abordagem foi aplicada com sucesso para a análise de amostras de leite e água de riacho, ambos fortificados com kanamicina, usando procedimento de extração em fase sólida com um polímero impresso molecularmente (MIP). A intensidade da fotoluminescência da nanopartícula cisteína-ZnS em solução contendo brometo de cetiltrimetilamônio (CTAB) foi reduzida (quenched) após adição de tiroxina. A redução total do sinal (quenching) seguiu o modelo de Stern-Volmer com resposta linear até 4,0 x 10-6 mol L-1 de concentração do analito, o LOD foi 6,2 x 10-8 mol L-1 (48,3 ng mL-1). A dispersão aquosa da cisteína-ZnS foi usada como sonda óptica para a determinação de tiroxina em formulações farmacêuticas e em saliva humana fortificada com analito. / [en] Recently, semiconductor nanocrystals, also known as quantum dots, have become very attractive for photoluminescence based sensing approaches due to their unique optical properties like intense photoluminescence with narrow profile, maximum wavelength adjustable by the control of particle size and higher photostability in comparison of conventional organic dyes. Different synthesized nanoparticles were evaluated as photoluminescent probes (as aqueous dispersions) for the determination of captopril, histamine, kanamycin and thyroxine (nonphotoluminescent analytes at room-temperature) avoiding the use of complex chemical derivatization procedures and enabling simple and sensitive quantifications. Thioglycolic acid (TGA) and 2-mercapoprionic acid (2MPA) modified CdTe nanoparticles and L-cysteine modified ZnS nanoparticles were synthesized via the colloid aqueous phase route. Their characterization was made using proper microscopic and spectroscopic methods. The emission intensity of 2MPA-Cdte is greatly enhanced in the presence of captopril. Under optimum conditions, the calibration model (Langmuir binding isotherm) was linear up to 4.8 x 10-4 mol L-1 with equilibrium binding constant of 3.2 x 104 L mol-1 and limit of detection (LOD) of 6.2 x 10-6 mol L-1 (1.3 (micro)g mL-1). Applications in captopril fortified human serum and in pharmaceutical formulations were demonstrated. The photoluminescence of TGA-CdTe nanoparticles was quenched by histamine in a concentration dependent manner (Stern-Volmer model). The linear response covered the concentration range up to 5.7 x 10-4 mol L-1 with LOD of 9.6 x 10-6 mol L-1 (1.1 (micro)g mL-1). The proposed method was used for the analysis of tuna fish. The presence of aminoglycosides enhanced the photoluminescence of the TGA-CdTe nanoparticles (following a Langmuir binding isotherm model). Kanamycin was used as a model aminoglycoside in order to study its effect on the photoluminescence enhancement of TGA-CdTe quantum dots dispersed in aqueous solution. The linear range extended up to 8.2 x 10-7 mol L-1 with LOD of 2.5 x 10-8 mol L-1 (14.2 ng mL-1). Binding constants were calculated for several aminoglycosides indicating that there is a relationship between the number of available primary amino groups and the increasing in photoluminescence. This approach was successfully applied for determination of kanamycin fortified milk and in stream water samples after solid phase extraction using a molecular imprinted polymer produced using a kanamycin template. The photoluminescence intensity of cysteine-ZnS in solution containing cetyltrimethyl ammonium bromide (CTAB) was quenched by thyroxine. The overall quenching followed a Stern-Volmer model with linear response coveing an analyte concentration range up to 4.0 x 10-6 mol L-1. LOD was 6.2 x 10-8 mol L-1 (48.3 ng mL-1). The aqueous dispersion of cysteine-ZnS was used as optical probe for the determination of thyroxine in pharmaceutical formulations and in analyte fortified human saliva.

The first part of this dissertation deals with the application of a luminescence quenching method to measure diffusion and permeation coefficients of oxygen in polymers. Most luminescence oxygen sensors do not follow linearity of the Stern-Volmer (SV) equation due to heterogeneity of luminophore in the polymer matrix, thus the complexity of data analysis is increased. To circumvent this limitation, inverted fluorescence microscopy is utilized in this work to investigate the SV response of the sensors at the micron-scale. In these diffusion experiments, oxygen concentration is measured by luminescence changes in regions with high SV constants and good linearity. Thus, we avoid numerical complexity of combining nonlinear SV equation with a diffusion model. This technique allows us to measure oxygen diffusion properties in different type of polymers like transparent, opaque, free-standing polymers and polymers that cannot be cast into free standing films and polymer composites. In the second part of this thesis, we have explored the effect of Ag-Cu alloy nanoparticles on the emission intensity of luminophores at their close proximity. Alloy nanoparticles offer additional degrees of freedom for tuning their optical properties by altering atomic composition and atomic arrangement and thus can be an attractive option for manipulating signal of a wide range of luminophores. In this work, surface plasmon resonance spectrum of Ag-Cu alloy nanoparticles deposited by sputtering was easily tuned in wide wavelength range by varying one experimental condition- annealing temperature. Large metal enhanced luminescence for different luminophores viz Alexa Fluor 594 and Alexa Fluor 488 were achieved at the vicinity of Ag-Cu nanoparticles when maximum spectral overlap between SPR spectra of Ag-Cu nanoparticles and the emission and absorption spectra of the luminophores occur. We also studied the effect of composition of Ag-Cu nanoparticles synthesized by the polyol process on the luminescence of low quantum yield dye Cy3. In the third part of this thesis, quenching effect of Cu nanoparticles on CdSe/ZnS nanocrystal quantum dots has been explored. As Cu nanoparticles have comparable dielectric properties with gold nanoparticles, they are expected to show similar quenching effects. It was found that Cu is an efficient quencher of fluorescence from CdSe/ZnS quantum dots and the quenching effect is due to resonance energy transfer from quantum dots to Cu nanoparticles.