Quantitative Polarization‐Resolved Second‐Harmonic‐Generation Microscopy of Glycine Microneedles

Abstract

amino acids, peptides, and proteins offers a noncontact, label-free and nondestructive method of obtaining a better understanding of disease processes both in vitro and in vivo. SHG has further applications in nanoscale characterization, [5] measurement of field-induced carrier motion in photonic devices, [6] and in the development of micro/nanoscale lasers. [7] Qualitative comparison of SHG conversion efficiency suffers from not having a clear benchmark of quantitative values of tensor elements. First principles modeling to obtain quantitative values of the susceptibility tensor such as time-dependent density functional theory is computationally demanding for typical ≥100 atom biomolecule cells and also needs to be benchmarked against experimental values. [8] The β and γ phases of glycine have been recently reported to possess high piezoelectric strain constants. [9] As both the strain and susceptibility tensors of a piezoelectric crystal have an equivalent third rank tensor form, the quantitative susceptibility tensor of glycine crystals provides a useful benchmark for SHG imaging of hierarchical structures in biology that could speed development of quantitative tissue imaging and diseases diagnosis. [10] Glycine is the simplest and only achiral amino acid with a single hydrogen as its side chain, NH 3 + CH 2 COO −. It crystallizes in three distinct phases under ambient conditions α, β, and γ. The carboxyl (COOH) and amino (NH 2) terminal groups become charged to form the zwitterion. [11] The α-phase crystallizes in space group P2 1 /c, comprising of centrosymmetric double layers of zwitterions linked via hydrogen bonds. [12] For this polymorph the presence of a center of symmetry precludes SHG. The β phase shows space group P2 1 and is composed of double layers of zwitterions but the molecular packing is noncentrosymmetric. The γ phase is also SHG active, crystallizing in the noncentrosymmetric trigonal space group P3 1, which forms a 3D molecular network with the zwitterions arranged in helices around the 3 1 screw axis. [13] The difference in properties between phases is due to the differing zwitterion stacking and internal bond angles. [14] Both of the noncentrosymmetric phases of glycine have shown potential as a biocompatible NLO material (Table S1, Supporting Information). A 21 µm thick layer of β glycine nanofibers has been shown to have a larger effective χ (2) relative to 600 µm particles of β glycine due to their subcoherence

Glycine: The Gift that Keeps on Giving

“…The γ-polymorph has also remarkable non-linear optical properties and can be used for second harmonic generation (SHG). [278][279][280][281] This property can also find biomedical applications, such as diagnostic imaging. SHG can provide disease diagnosis through characterization of biological building blocks.…”

“…A comparison of the SHG susceptibility tensors of βand γ-phase glycine microneedles gave the maximum nonlinear susceptibility coefficients d 33 = 15 pm V À 1 for the β and d 33 = 5.9 pm V À 1 for the γ phase. [278] One of the major advantages of glycine-based materials is their ability to biodegrade without polluting the environment or poisoning a living organism. Electronics wastes (e-wastes) are the major concern in the rapid expansion of smart/ wearable/portable electronics in modern high-tech society.…”

Ferroelectricity in glycine: A mini-review

“…On a completely different scale, glycine has been found in the interstellar medium (Kuan et al, 2003;Ioppolo et al, 2021) and in the comas of comets and meteorites, (Elsila et al, 2009;Altwegg et al, 2016) thus providing evidence of the panspermia hypothesis (Wesson, 2010). As for the functional physical properties of crystalline glycine, they largely depend on the supramolecular packing of its molecules into three main polymorphs (α, β, and γ), resulting in different crystallographic structures (Heredia et al, 2012;Guerin et al, 2017;Gleeson et al, 2020;Boldyreva, 2021). It has been a long time established that the α-phase is centrosymmetric (space group P2 1 /n), in which only surface piezoelectricity and pyroelectricity may exist via doping or water incorporation (Piperno et al, 2013;Meirzadeh et al, 2018;Dishon et al, 2020).…”

Ab-Initio Predictions of the Energy Harvesting Performance of L-Arginine and L-Valine Single Crystals

“…It is unique amongst biomolecular crystals in that the predicted electronic and ionic contributions to the piezoelectric tensor are both high but of opposite polarity, resulting in these reduced values. This also explains why valine has a low piezoelectric response, but high non-linear optical performance (Moitra and Kar, 2010), as we have recently demonstrated that the second harmonic generation capabilities of small biomolecular crystals correlates to the electronic contribution to the piezoelectric tensor only (Gleeson et al, 2020).…”