Construction of Triboelectric Series and Chirality Detection of Amino Acids Using Triboelectric Nanogenerator

Abstract Triboelectrification necessitates a frictional interaction between two materials, and their contact electrification is characteristically based on the polarity variance in the triboelectric series. Utilizing this fundamental advantage of the triboelectric phenomenon, different materials can be identified according to their contact electrification capability. Herein, an in‐depth analysis of the amino acids present in the stratum corneum of human skin is performed and these are quantified regarding triboelectric polarization. The principal focus of this study lies in analyzing and identifying the amino acids present in copious amounts in the stratum corneum to explain their positive behavior during the contact electrification process. Thus, an augmented triboelectric series of amino acids with quantified triboelectric charging polarity by scrutinizing the transfer charge, work function, and atomic percentage is presented. Furthermore, the chirality of aspartic acid as it is most susceptible to racemization with clear consequences on the human skin is detected. The study is expected to accelerate research exploiting triboelectrification and provide valuable information on the surface properties and biological activities of these important biomolecules.


Amino acid
At. % of N At.% of O At. % of C L-Arginine L-Histidine L-Serine L-Glutamine L-Threonine L-Asparagine L-Glutamic acid L-Aspartic acid  S1.Atomic percentages of amino acids with charged and polar uncharged sidechains.      14]

Figure S1 .
Figure S1.Characterization and work function estimation by the DFT calculations of amino acids with positively charged sidechains.XRD patterns of a) L-arginine and c) L-histidine.The simulated work function and unit-cell structure of b) L-arginine (0 3 1) and d) L-histidine (1 0 2).

Figure S2 .
Figure S2.Characterization and work function estimation by the DFT calculations of amino acids with negatively charged sidechains.XRD patterns of a) L-glutamic acid and c) Laspartic acid.The simulated work function and the unit-cell structure of b) L-Glutamic acid (0 1 2) and d) L-aspartic acid (1 0 1).

Figure S3 .
Figure S3.Characterization and work function estimation by the DFT calculations of uncharged polar amino acids.XRD patterns of a) L-serine and c) L-threonine.The simulated work function and the unit-cell structure of b) L-serine (1 3 2) and d) L-threonine (0 1 1).

Figure S4 .
Figure S4.Characterization and work function estimation by the DFT calculations of uncharged polar amino acids (amide sidechain).XRD patterns of a) L-glutamine and c) Lasparagine.The simulated work function and the unit-cell structure of b) L-glutamine (3 1 1) and d) L-asparagine (1 0 2).

Figure S5 .
Figure S5.XPS characterization of amino acids with positively charged sidechains.Survey spectra of a) L-arginine and b) L-histidine.High-resolution core level photoemission spectra c) N1s of L-arginine, d) O1s of L-arginine, e) C1s of L-arginine, f) N1s of L-histidine, g) O1s of L-histidine, and h) C1s of L-histidine.Herein, black dots represent experimental data, whereas by summing the Gaussian-Lorentzian fits related to respective components, the final fit was obtained and represented by the continuous bold black line (various moieties are

Figure S6 .
Figure S6.XPS characterization of amino acids with negatively charged sidechains.Survey spectra of a) L-glutamic acid and b) L-aspartic acid.High-resolution core level photoemission spectra c) N1s of L-glutamic acid, d) O1s of L-glutamic acid, e) C1s of L-glutamic acid, f) N1s of L-aspartic acid, g) O1s of L-aspartic acid, and h) C1s of L-aspartic acid.Herein, black dots represent experimental data, whereas by summing the Gaussian-Lorentzian fits related to respective components, the final fit was obtained and represented by the continuous bold black line (various moieties are represented in different colors under the spectra).

Figure S7 .
Figure S7.XPS characterization of amino acids with polar uncharged sidechains.Survey spectra of a) L-serine and b) L-threonine.High-resolution core level photoemission spectrum c) N1s of L-serine, d.O1s of L-serine, e) C1s of L-serine, f) N1s of L-threonine, g) O1s of Lthreonine, and h) C1s of L-threonine.Herein, black dots represent experimental data, whereas by summing the Gaussian-Lorentzian fits related to respective components, the final fit was obtained and represented by the continuous bold black line (various moieties are represented in different colors under the spectra).

Figure S8 .
Figure S8.XPS characterization of amino acids with polar uncharged sidechains (amide sidechains).Survey spectra of a) L-glutamine and b) L-asparagine.High-resolution core level photoemission spectrum c) N1s of L-glutamine, d) O1s of L-glutamine, e) C1s of Lglutamine, f) N1s of L-asparagine, g) O1s of L-asparagine, and h) C1s of L-asparagine.Herein, black dots represent experimental data, whereas by summing the Gaussian-Lorentzian fits related to respective components, the final fit was obtained and represented by the continuous bold black line (various moieties are represented in different colors under the spectra).

Figure S9 .
Figure S9.Characterization and work function estimation by DFT calculations.XRD patterns of a) L-proline and c) glycine.Simulated work functions and the unit-cell structures of b) Lproline (0 2 1) and d) Glycine (0 0 1).

Figure S10 .
Figure S10.Characterization and work function estimation by DFT calculations.XRD patterns of a) L-alanine and c) L-cysteine.Simulated work functions and unit-cell structures of b) L-alanine (1 1 1) and d) Cysteine (0 0 3).

Figure S11 .
Figure S11.XPS characterization of amino acids with special and hydrophobic sidechains.Survey spectra of a) Glycine and b) L-proline.High-resolution core level photoemission spectrum c) N1s of glycine, d) O1s of glycine, e) C1s of glycine, f) N1s of L-proline, g) O1s of L-proline, and h) C1s of L-proline.Herein, black dots represent experimental data, whereas by summing the Gaussian-Lorentzian fits related to respective components, the final fit was obtained and represented by the continuous bold black line (various moieties are represented in different colors under the spectra).

Figure S12 .
Figure S12.XPS characterization of amino acids with special and hydrophobic sidechains.Survey spectra of a) L-cysteine and b) L-alanine.High-resolution core level photoemission spectra c) S2p of L-cysteine, d) N1s of L-cysteine, e) O1s of L-cysteine, f) C1s of L-cysteine, g) N1s of L-alanine, and h) O1s of L-alanine, i) C1s of L-alanine.Herein, black dots represent experimental data, whereas by summing the Gaussian-Lorentzian fits related to respective components, the final fit was obtained and represented by the continuous bold black line (various moieties are represented in different colors under the spectra).

Figure S13 .
Figure S13.Relationship between the transfer charge density during contact electrification and the relative work functions of the amino acids with PTFE.

Figure S14 .
Figure S14.The triboelectric series of amino acids.

Figure S15 .
Figure S15.Pie chart representation of the constituent amino acids of the human stratum corneum.[1,3]

Figure S17 .
Figure S17.Experimental setup.a) digital image of atomic force microscopy (AFM) system with the dehumidifying system, b) digital image of the electrical output measurement system.