InAs Nanocrystals Core-Shell NIR Imaging
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Solution Overview
Problem
Current semiconductor nanocrystals for biological imaging face challenges in optimizing size, stability, quantum yield, derivatization, and non-specific binding, limiting their effectiveness in deep tissue imaging and single-particle tracking applications.
Innovation Solution
Development of water-soluble semiconductor nanocrystals with a core-shell structure, specifically InAs cores coated with a ZnCdS shell, and functionalized with poly(amino-PEG) ligands for enhanced stability and selective binding, allowing for deep tissue imaging and targeted conjugation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If nanocrystal size is decreased to enable single-particle tracking, then tracking precision is improved, but quantum yield and emission intensity deteriorate
Solution Approach 1:
The patent applies a core-shell structure where a small InAs nanocrystal core (2-5 nm) is nested within a larger ZnCdS shell. This nested configuration allows the core to maintain small size for single-particle tracking while the shell provides enhanced quantum confinement and increased quantum yield, resolving the contradiction between size and emission intensity
Solution Approach 2:
The patent uses composite materials by combining InAs core with ZnCdS shell, creating a heterostructure with type-I band alignment. This composite approach enables the small core to maintain quantum confinement for tracking precision while the shell material enhances radiative recombination efficiency, improving emission intensity without increasing hydrodynamic size
2Length of stationary object
If nanocrystal size is decreased for deep tissue imaging, then tissue penetration is improved, but quantum yield deteriorates
Solution Approach 1:
The small InAs core (2-5 nm) nested within the ZnCdS shell enables deep tissue penetration through minimal scattering while the shell's type-I band structure enhances quantum yield by confining both electrons and holes in the core, resolving the contradiction between size and quantum yield
Solution Approach 2:
The patent changes material parameters by selecting InAs with a narrow bulk band gap (0.36 eV) and combining it with ZnCdS shell, creating quantum confined structures with tunable emission wavelengths in the 700-1000 nm range optimized for deep tissue imaging while maintaining high quantum yield
3Adaptability or versatility
If nanocrystals are functionalized for selective binding, then targeting capability is improved, but non-specific binding increases
Solution Approach 1:
The patent applies local quality by placing PEG ligands on the outer surface of the nanocrystal shell, creating a hydrophilic, non-fouling surface that reduces non-specific binding, while leaving the core and shell structure intact for maintaining quantum yield and enabling selective targeting through surface functionalization
4Reliability
If core diameter is decreased to 1.4 nm or less, then quantum confinement is enhanced, but manufacturing precision requirements increase
Solution Approach 1:
The patent nests the small InAs core (1.4 nm or less) within the ZnCdS shell, which provides structural stability and protects the small core from aggregation and degradation, enabling enhanced quantum confinement while reducing the practical manufacturing precision requirements through the protective shell environment
Solution Approach 2:
The patent changes the synthesis approach by using hot-injection methods with controlled temperature profiles and specific precursor ratios to achieve precise core diameter control at 1.4 nm or less, then stabilizes this size through shell growth, maintaining quantum confinement while achieving reproducible manufacturing
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The nanocrystals achieve high quantum yield, stability, and reduced non-specific binding, enabling effective deep tissue imaging and targeted labeling with minimal background interference, as demonstrated by multiphoton microscopy in vivo and in vitro applications.
Implementation Method 1
Nanocrystals of semiconductor materials having sufficiently small dimensions can exhibit quantum confinement of excitons (excited state electron-hole pair) in all three dimensions. Quantum confinement leads to an increase in the effective band gap of the material with decreasing crystallite size.
Implementation Method 2
The quantum efficiency of emission from nanocrystals having a core of a first semiconductor material can be enhanced by applying an overcoating of a second semiconductor material such that the conduction band of the second semiconductor material is of higher energy than that of the first semiconductor material, and the valence band of the second semiconductor material is of lower energy than that of the first semiconductor material. As a result, both charge carriers of an exciton, i.e., electrons and holes, are confined in the core of the nanocrystal.
Implementation Method 3
both the optical absorption and emission of nanocrystals shift to the blue (i.e., to higher energies) as the size of the nanocrystal decreases
Data Source
AI summary
Water soluble InAs(ZnCdS) semiconductor nanocrystals with bright and stable emission in the near infrared (NIR) wavelength range have been prepared. The NIR semiconductor nanocrystals can be functionalized to enable imaging of specific cellular proteins. In addition, the utility of the NIR region for in vivo biological imaging is clearly demonstrated by the superior ability of InAs(ZnCdS) semiconductor nanocrystals to image tumor vasculature.