Efficient Infrared‐Emitting PbS Quantum Dots Grown on DNA and Stable in Aqueous Solution and Blood Plasma

Abstract

Quantum-dot nanocrystals have been used to label single molecules during living-cell assays [1] and provide direct visual guidance and real-time confirmation of complete resection during cancer surgery in an animal model. [2] The use of quantum dots for deep-tissue imaging accompanied by low autofluorescence in vivo requires emission in the second infrared biological window of 1000±1200 nm combined with stability in biological media. Surface chemistry determines the chemical and optical stability of quantum dots. A stabilizing outer shell minimizes diffusion of oxygen to the surface of the core of the nanoparticle, as demonstrated using a high-bandgap semiconductor shell [3] and a dielectric shell.[4] Silanized nanoparticles have been shown to be water soluble and to retain the absorption and emission spectra of the original particles; however, the nanoparticles lost 60±80 % of their original quantum efficiency in this process. Recently, oligomeric phosphines [5] have been employed to form three thin concentric sublayers around quantum dots: an inner phosphine layer for dot-surface passivation, a linking layer for protection, and an outer functionalized layer for miscibility and subsequent chemical modification or conjugation to biomolecules. In the infrared, the application of this multistep synthetic method to type-II core±shell nanoparticles has resulted in quantum dots that show modest degradation in 37 C plasma over the course of half an hour.[3]Here we adopt an entirely different strategy: we report the first growth of efficient infrared photoluminescent quantum dots directly on a DNA template. Our infrared-emitting quantum dots grown on the biomolecular template are efficient and stable in water, serum, and blood plasma.DNA has previously been decorated with metal nanoparticles 5±10 nm in diameter through the use of thiol linkages. [6] DNA has also been used as a long-term stabilizer and template in the growth of CdS nanocrystals, but with no reports of a photoluminescence quantum efficiency.[7±10] Related progress has also been made in synthesizing CdS nanoparticles in which growth was carried out at room temperature followed by annealing at 80 C to improve photoluminescent properties; quantum efficiencies of 10 ±4 were estimated.[11] The only previous report of DNA-templated growth on PbS has yielded materials with no detectable luminescence in the infrared.[12]We worked instead at a synthesis temperature at which chemical interaction was possible between the metal cations used in PbS growth and at least two classes of sites on DNA: the phosphate backbone, and also DNA's purine and pyrimidine bases. The bases provide an additional opportunity for control over the growth of nanoparticles and the passivation of their surface states. The synthesis reported herein is simple, reproducible, and yields PbS nanoparticles with exceptional stability and photoluminescence quantum efficiency. Energyfiltered transmission electron microscopy (EFTEM) reveals cubic-latticed PbS quantum dots 4 nm in diameter on a network...

Metal, Metalloid, and Oxide Nanoparticles for Therapeutic and Diagnostic Oncology

“…The biogenic system is not limited to using bacteria, actinomycetes, fungi, and yeasts to produce NPs; instead, plant or algae extracts and even informational biomacromolecules, including proteins, polypeptides, DNA, and RNA (as other sources of biological materials), can also be applied to produce NPs [51]. For example, informational biomolecules (DNA and RNA) can be applied as building blocks capable of potentially supplying a set of chemical functional groups (e.g., phosphate backbones) that hinder the size and shape control of biomineralized nanomaterials [64,65].…”

Infrared Quantum Dots

“…The growth of PbS nanoparticles on a DNA template has recently been demonstrated to result in efficient infrared fluorophores which are stable in blood plasma at 37 C for over one week. [11] Quantum dots were grown on single-stranded DNA, as revealed in elementally resolved high-resolution TEM. The DNA phosphate backbone and imino protons provided sites for passivation and solubilization of the nanocrystals in aqueous solution.…”

Temperature dependence of the photoluminescence emission from thiol-capped PbS quantum dots

“…6 Of the various nanocrystals, PbS-based QDs have emerged as promising candidates for optical applications in the near-infrared region of the electromagnetic spectrum. 5,[7][8][9] In particular, since the emission wavelength of PbS dots can be controlled and tailored within the spectroscopic window of 1.0-1.2 m of low absorption of biological systems, water soluble PbS nanocrystals have the potential to be used as biocompatible fluorescent labels and to replace traditional organic fluorescent dyes.The effect of temperature T on the optical properties of PbS quantum dots is of great importance for their use in room temperature ͑RT͒ applications. Recently, an unusually large linewidth ͑ϳ100 meV͒ for the RT photoluminescence ͑PL͒ emission from an individual PbS QD was reported.…”