Structure and Morphology-Controlled Synthesis of Colloidal Ge 1– x – y Si y Sn x Quantum Dots with Composition-Tunable Energy Gaps and Visible to Near-IR Optical Properties
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-10-16 |
| Journal | ACS Materials Au |
| Authors | Chineme Jeanfrances Onukwughara, D. Pate, Yasmitha A. Alahakoon, Ümit Özgür, Indika U. Arachchige |
| Institutions | Virginia Commonwealth University |
| Analysis | Full AI Review Included |
Near-Infrared Fluorescence from Nanodiamond for Multimodal Bioimaging: Technical Analysis and 6CCVD Material Solutions
Section titled “Near-Infrared Fluorescence from Nanodiamond for Multimodal Bioimaging: Technical Analysis and 6CCVD Material Solutions”This document analyzes the research focusing on using Nickel (Ni)-related color centers in nanodiamonds (ND) for bioimaging applications due to their stable near-infrared (NIR) fluorescence. This capability positions high-quality synthetic diamond as a critical component in next-generation biomedical optics and biosensing.
Executive Summary
Section titled “Executive Summary”The following points summarize the core technical achievements and the resulting value proposition of using Ni-related centers for bioimaging:
- Autofluorescence Mitigation: The Ni-related 1.4 eV color center exhibits stable emission at 885 nm (NIR region), successfully avoiding the major limitation of traditional NV center imaging by operating far outside the 400-550 nm biological autofluorescence range.
- Dual Excitation Capability: Fluorescence is successfully demonstrated using both one-photon (325 nm, 532 nm) and two-photon (760 nm femtosecond laser) excitation, offering versatility for different imaging depths and spatial resolutions.
- Enhanced Safety and Transparency: Shifting emission and excitation into the NIR region provides higher transparency for biological objects and uses lower-energy laser excitation, resulting in decreased photobleaching and phototoxicity compared to visible-light probes.
- Material Optimization Insight: The study shows that the photoluminescence (PL) intensity of the 1.4 eV Ni center, relative to other color centers, is significantly higher in larger diamond particles (up to 25 µm), informing optimal material size selection for probe design.
- In Vivo Application Demonstrated: Successful fluorescence mapping of 500 nm carboxylated NDs localized within Baby Hamster Kidney (BHK) cells confirms the applicability of Ni-related centers for ambient-condition bioimaging without causing cell damage.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Primary Emission Wavelength (Ni-Center) | 885 | nm | 1.4 eV color center; Near-Infrared (NIR) region |
| Excitation Laser (Two-Photon) | 760 | nm | Femtosecond Ti:Sapphire Laser |
| Two-Photon Pulse Duration | 140 | fs | Used for high-resolution deep tissue analysis |
| Two-Photon Repetition Rate | 80 | MHz | Input laser power 96 mW |
| One-Photon Excitation Wavelengths | 325 / 532 | nm | He-Cd Gas Laser / Solid State Laser |
| NV⁻ Center Zero-Phonon Line (ZPL) | 637 | nm | Overlaps with biological autofluorescence range |
| ND Particle Sizes Tested | 100 nm, 500 nm, 2.5 µm, 25 µm | - | Used to analyze size-dependent emission variability |
| Ni-Center PL Collection Range | 800-1200 | nm | Detection window used to isolate 1.4 eV defect signal |
| Imaging Temperature | Ambient (295) / Low (110) | K | Low temperature used to resolve doublet splitting (883/885 nm) |
| Cell Line Used | BHK | - | Baby Hamster Kidney cells for bioimaging validation |
Key Methodologies
Section titled “Key Methodologies”The following is an overview of the critical steps and parameters used to synthesize, characterize, and apply the Ni-doped nanodiamonds:
- Material Sourcing & Pretreatment:
- Synthetic diamond powders (Kay Diamond, USA) ranging from 100 nm to 2.5 µm were utilized, implying HPHT growth origin (where nickel catalysts are inherently included).
- Diamond powders were carboxylated using strong acid treatments to ensure surface functionalization, remove metallic/non-diamond carbon impurities, and enhance biocompatibility.
- Spectroscopic Characterization:
- Raman and PL Spectroscopy: Conducted using a confocal micro-Raman spectrometer with 532 nm (2 mW) and 325 nm (20 mW) laser excitations.
- Low-Temperature Analysis: Samples were mounted in a Linkam variable temperature stage (THMS 600) to stabilize measurements at 110 K, allowing for clearer resolution of color center fine structure.
- Two-Photon Measurements: Performed using femtosecond tunable 760 nm excitation (140 fs pulse duration) with a single photon counting system (PicoHarp 300) for detection in the 800-1000 nm spectroscopic range.
- Bioimaging Protocol:
- Cell Incubation: BHK cells were co-incubated with 500 nm ND for 8 hours at 37°C in a humidified incubator (5% CO2).
- Imaging: Laser Confocal Scanning Microscopy (Leica TCS SP5) was used, equipped with Argon laser (488 nm excitation) for general cellular imaging, and separate excitation (325 nm) was used for PL mapping.
- Defect Mapping: PL mapping isolated the Ni-related center signal by collecting in the 800-1200 nm range, providing clear spatial localization of NDs relative to cell boundaries.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD provides the material foundation necessary to replicate and extend this pioneering research in NIR diamond bioimaging. Our specialized MPCVD growth techniques offer superior control over purity, defect incorporation, and geometry compared to traditional HPHT diamond powders.
Applicable Materials for NIR Bioimaging
Section titled “Applicable Materials for NIR Bioimaging”To achieve optimal, reproducible NIR fluorescence using Ni-related centers, high-purity, low-strain diamond material is essential.
| Application Requirement | 6CCVD Recommended Material | Rationale & Advantage |
|---|---|---|
| High-Purity Starting Material | Optical Grade Single Crystal Diamond (SCD) | SCD wafers (0.1µm to 500µm thickness) provide ultra-low defect backgrounds, ensuring that synthesized Ni-centers are the dominant emission source, increasing contrast and signal-to-noise ratio. |
| High-Density Sensing Array | Polycrystalline Diamond (PCD) Plates | We offer PCD plates up to 125 mm diameter with Ra < 5 nm polishing. These substrates are ideal for scalable production of large-area bio-sensors or microfluidic chips utilizing the NIR emission. |
| Tunable NIR Center Incorporation | Custom Doping via MPCVD | While the paper utilizes native Ni incorporation from HPHT growth, 6CCVD can integrate Ni or Nitrogen impurities directly during MPCVD growth, allowing for precise control over the density and homogeneity of the 1.4 eV (Ni) and NE² (Ni-N complex) centers. |
| Electrochemical Sensing Integration | Boron-Doped Diamond (BDD) Films | BDD, available up to 500 µm, provides robust, chemically inert electrodes. Combining the NIR fluorescence of Ni-centers with the electrochemical properties of BDD creates advanced, multimodal biosensors. |
Customization Potential for Biomedical Engineers
Section titled “Customization Potential for Biomedical Engineers”The flexibility of the 6CCVD MPCVD platform directly addresses the experimental needs outlined in this research:
- Custom Dimensions and Etching: While the paper used loose powders, 6CCVD can supply bulk SCD/PCD material up to 125 mm. We offer advanced laser cutting and plasma etching services to create high-uniformity diamond microparticles or complex structures tailored for specific cellular internalization studies or device integration.
- Surface Functionalization Ready: The experiment utilized carboxylated NDs. 6CCVD provides ultra-low roughness polishing (Ra < 1nm for SCD), creating chemically pristine surfaces ready for superior functionalization (e.g., covalent bonding for drug delivery or biocompatibility coatings).
- Integrated Metalization Services: For device integration (e.g., on-chip biosensing, electrical addressing), 6CCVD offers in-house metal deposition including Ti, Pt, Au, Pd, W, and Cu, eliminating the need for external processing steps.
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team specializes in defect engineering and MPCVD growth optimization. We can assist researchers in selecting the precise material specifications (e.g., target Ni-doping concentration, post-growth annealing profiles) required to maximize the stable Near-Infrared fluorescence output for similar bioimaging or quantum sensing projects. Our expertise ensures reliable material performance under demanding conditions, such as high-power femtosecond laser exposure.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Ge<sub>1-<i>x</i>-<i>y</i></sub> Si <sub><i>y</i></sub> Sn <sub><i>x</i></sub> quantum dots (QDs) are an attractive class of low-to-nontoxic and earth-abundant semiconductors exhibiting size and composition-tunable optical properties. Their electronic structure can be modified by varying elemental composition and quantum confinement to achieve tunable absorption and photoluminescence (PL) across the visible to near-IR spectrum. Alloying with Sn enhances oscillator strengths, whereas decreasing size and incorporating Si increase energy gaps. Herein, we report a facile colloidal route to produce Ge<sub>1-<i>x</i>-<i>y</i></sub> Si <sub><i>y</i></sub> Sn <sub><i>x</i></sub> QDs with narrow size dispersity (4.0 ± 0.4 - 5.2 ± 0.6 nm) and variable Si (<i>y</i> = 0.030 - 0.252) and Sn (<i>x</i> = 0.044 - 0.059) compositions and investigate the influence of core/surface species on optical properties. Structural analysis reveals an expanded diamond cubic Ge lattice, a red-shifted Ge-Ge Raman peak, and the emergence of a Ge-Si peak with increasing Si composition. Successful alloying of Si and Sn into Ge host lattice is confirmed by electron microscopy, suggesting homogeneous solid solution behavior of ternary QDs. Surface analysis further indicates the presence of Ge<sup>0</sup>/Si<sup>0</sup>/Sn<sup>0</sup> core species alongside charged Ge <sup><i>n</i>+</sup>/Si <sup><i>n</i>+</sup>/Sn <sup><i>n</i>+</sup> (1 ≤ <i>n</i> ≥ 4) surface species coordinated to passivating organic ligands. The effects of confinement and surface/core elemental composition on optical properties were revealed through composition-tunable absorption onsets (1.15 - 2.33 eV) and associated Tauc direct (1.86 - 3.03 eV) and indirect (1.01 - 1.81 eV) energy gaps achieved for QDs with <i>x</i> = 0.044 - 0.059 and <i>y</i> = 0.030 - 0.252, which are prominently blue-shifted from bulk counterparts and previously reported Ge<sub>1-<i>x</i></sub> Sn <sub><i>x</i></sub> QDs. PL spectra of Ge<sub>1-<i>x</i>-<i>y</i></sub> Si <sub><i>y</i></sub> Sn <sub><i>x</i></sub> QDs exhibit nanosecond-scale emission from 1.84 - 1.88 eV for <i>y</i> ≤ 0.134 and 2.32 - 2.43 eV for <i>y</i> ≥ 0.177 compositions, displaying similarly pronounced blueshifts from comparable Ge<sub>1-<i>x</i></sub> Sn <sub><i>x</i></sub> QDs. This correlated absorption/PL tunability expands upon that demonstrated by Ge and Ge<sub>1-<i>x</i></sub> Sn <sub><i>x</i></sub> counterparts widens the optical window of Group IV semiconductor nanostructures, making them attractive for visible-to-near-IR optoelectronic studies.