| Summary: | The objective of this work is two-fold; investigation of the electrochemical and electrochemiluminescent (ECL) properties of near-infrared (NIR) quantum dots (QDs) in buffer and whole blood; and their subsequent incorporation into ECL biosensing systems with potential application in whole blood analysis. QDs exhibited size-dependent optical and electrochemical properties with the largest QDs demonstrating ECL emission in the NIR region (811 nm). This should improve light penetration through whole blood, a prediction that has not yet been investigated for the ECL process. NIR QDs were shown to be flexible ECL emitters and optimisation of system parameters was implemented to obtain maximum ECL performance. This was achieved using a QD-chitosan film on a glassy carbon electrode with potassium persulfate co-reactant in phosphate buffered saline at pH 7.4. Intense reductive and oxidative ECL signals were generated directly in whole blood, which was at least ten times more intense than t hat achieved using visible region emitting QDs. The response exhibited sensitivity to blood samples spiked with clinically relevant analytes, homocysteine and dopamine, establishing the viability of NIR ECL as a detection method from whole blood. To expand the integration of NIR QDs into biosensing systems, a selective biosensor for cholesterol was developed that exhibited good stability, specificity and a clinically relevant linear range (1-5 mM). Detection in human serum was possible, however, radical quenching in whole blood limited its use as a biosensor in this environment in its current form, demonstrating the complications that can arise with analysis from such a complex matrix. For that reason, an alternative biosensor design that used conditions optimised in earlier work was used to improve system sensitivity. Fabrication of an immunosensor for IgG resulted in an ECL signal that was detected in whole blood. Following significant development, it is envisaged such a system can form the basis of a new generation of NIR ECL biosensors capable of detection directly from whole blood.
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