First-Principles Calculations for Glycine Adsorption Dynamics and Surface-Enhanced Raman Spectroscopy on Diamond Surfaces

At a Glance

Metadata	Details
Publication Date	2025-03-27
Journal	Nanomaterials
Authors	Shiyang Sun, Chi Zhang, Peilun An, Pingping Xu, Wenxing Zhang
Institutions	Baogang Group (China), Inner Mongolia University of Science and Technology
Analysis	Full AI Review Included

Executive Summary

This study utilized first-principles calculations (DFT and AIMD) to evaluate the stability and Surface-Enhanced Raman Spectroscopy (SERS) performance of glycine (Gly) adsorbed on the diamond (100) surface, positioning diamond as a high-potential biointerface material.

Optimal Adsorption Structure: The carboxyl-terminated adjacent-dimer phenyl-like ring (CAR) configuration was identified as the most stable structure, exhibiting the highest adsorption energy (5.03 eV) and the shortest interface distance (1.37 Angstrom).
Stability Mechanism: The high stability of the CAR configuration is attributed to the formation of strong polar covalent bonds between the carboxyl O atoms and the diamond surface C atoms, confirmed by p-p orbital hybridization.
Thermal Dynamics (AIMD): Molecular dynamics simulations (300 K to 500 K) confirmed that the stable CAR structure only undergoes simple thermal vibrations. Metastable configurations (ATO and CTR) evolve under thermal energy, transforming into the more stable, benzene-ring-like CAR structure.
SERS Performance: The diamond substrate significantly enhances the Raman signal of adsorbed glycine molecules, achieving a maximum enhancement amplitude exceeding 200 times. The average enhancement amplitude was greater than 50 times.
Signal Selectivity: The SERS effect is highly selective, with the characteristic peaks related to the carboxyl (COO) and amino (NH₂) groups exhibiting the most pronounced enhancement and a noticeable blue shift.
Value Proposition: Diamond offers exceptional adsorption capabilities and strong SERS characteristics, making it a promising alternative material for high-sensitivity biodetection and biointerfaces.

Technical Specifications

Parameter	Value	Unit	Context
Most Stable Adsorption Energy (CAR)	5.03	eV	First-principles calculation (DFT)
Shortest Interface Distance (CAR)	1.37	Angstrom	Average adsorption distance (l_avg)
Maximum SERS Enhancement	>200	Times	Observed for carboxyl and amino group peaks
Average SERS Enhancement	>50	Times	Overall enhancement factor
AIMD Temperature Range	300, 400, 500	K	Canonical NVT ensemble simulation
CAR Max Bond Length Fluctuation (Δd_max)	0.22	Angstrom	Structural change upon adsorption
CAR Max Bond Angle Adjustment (Δθ_max)	10.2	Degrees	Structural change upon adsorption
Glycine C=O Vibration Peak (Unadsorbed)	1763	cm^-1	Characteristic peak disappears upon adsorption
Diamond Surface Reconstruction	(2 x 1)	N/A	Adopted structure for the (100) surface
DFT Cutoff Energy	450	eV	Plane-wave basis set parameter

Key Methodologies

Model Construction: A slab model was used, consisting of five layers of diamond crystal. The bottom two layers were fixed and H-terminated to eliminate surface polarity, while the top three layers were relaxed.
Surface Preparation: The diamond (100) surface was modeled using the widely accepted (2 x 1) reconstruction structure, featuring adjacent surface carbon dimers.
DFT Calculation: Calculations were performed using the VASP 6.4.1 software package, employing the Generalized Gradient Approximation (GGA) with the PBE exchange-correlation functional.
Simulation Parameters: A cutoff energy of 450 eV and a 3 x 3 x 1 k-point grid were implemented. Ion energies were converged to a threshold of 1 x 10^-5 eV.
Ab Initio Molecular Dynamics (AIMD): Simulations utilized a Canonical NVT ensemble system to study temperature effects on adsorption dynamics.
Thermal Testing: Environmental temperatures were set at 300 K (room temperature), 400 K, and 500 K. Each simulation ran for 10 ps, with a 1 fs time step, totaling 10,000 steps.
Structural Analysis: The structural evolution of glycine was quantified using Root Mean Square Deviation (RMSD) analysis.
Raman Spectra Generation: Raman spectral information was derived from the Raman tensor, calculated via polarizability calculations of vibrational modes under the two-harmonic approximation.

Commercial Applications

High-Sensitivity Biosensing: Diamond substrates are ideal for developing advanced SERS biosensors capable of detecting biological single molecules with high sensitivity, accuracy, and specificity, particularly for organic molecules with weak inherent Raman signals (like glycine).
Biocompatible Coatings and Implants: The exceptional stability and strong adsorption characteristics of the CAR configuration on diamond (100) make it suitable for use as a stable biointerface coating on medical implants, promoting controlled cell adhesion and integration.
Nanodiamond Probes: Nanodiamonds, which exhibit distinct surface Raman characteristics, can be functionalized using the stable CAR structure for use in clinical medicine as magnetic resonance imaging, photoacoustic imaging, and fluorescence imaging probes.
Chemical Detection and Analysis: The selective SERS enhancement observed for carboxyl and amino groups provides a mechanism for targeted detection and analysis of specific functional groups in complex biological or chemical samples.
High-Temperature Bio-Processing: The stability of the CAR configuration across temperatures up to 500 K suggests diamond substrates can maintain functionality during high-temperature sterilization or processing steps required in medical device manufacturing.

View Original Abstract

Based on first-principles calculations, the stability of three adsorption configurations of glycine on the (100) surface of diamonds was studied, leading to an investigation into the surface-enhanced Raman scattering (SERS) effect of the diamond substrate. The results showed that the carboxyl-terminated adsorption configuration (CAR) was the most stable and shortest interface distance compared to other configurations. This stability was primarily attributed to the formation of strong polar covalent bonds between the carboxyl O atoms and the surface C atoms of the (100) surface of diamonds. These results were further corroborated by first-principles molecular dynamics simulations. Within the temperature range of 300 to 500 K, the glycine molecules in the carboxyl-terminated adjacent-dimer phenyl-like (CAR) configuration exhibited only simple thermal vibrations with varying amplitudes. In contrast, the metastable ATO and carboxyl-terminated trans-dimer phenyl-like ring (CTR) configurations were observed to gradually transform into benzene-ring-like structures akin to the CAR configuration. After adsorption, the intensity of glycine’s characteristic peaks increased substantially, accompanied by a blue shift phenomenon. Notably, the characteristic peaks related to the carboxyl and amino groups exhibited the highest enhancement amplitude, exceeding 200 times, with an average enhancement amplitude exceeding 50 times. The diamond substrate, with its excellent adsorption properties and strong surface Raman spectroscopy characteristics, represents a highly promising candidate in the field of biomedicine.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano15070502

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