Brightness-Equalized Heavy Metal-Free Quantum Dots For Biosensing And Imaging

Semiconductor quantum dots (QDs) have great potential for multiplexed imaging and biosensing applications. Due to the quantum confinement effect, spectral tuning of the emission color of these nanocrystals is made possible through changing their size. However, QDs of different emission colors are dissimilar in their brightness values, defined as the product of molar extinction coefficient (E) and quantum yield (QY). These differences arise from extinction coefficients which are coupled to the number of atoms and bonds constituting the QD. As a consequence, the relative brightness of QDs can be orders of magnitude higher for larger, red emitting QDs compared to their smaller blue/green emitting counterparts even with comparable QYs. This study addresses this problem by drawing a quantitative comparison of absorption properties of different type-I InP QDs, aiming to make these heterostructures suitable for accurate imaging and sensing applications. Tuning of the absorption cross-section and extinction coefficients, along with brightness tuning of the QDs has been performed through synthesizing a series of QDs with a combination of core sizes, shell thicknesses, and compositions.