machine-learning-assisted-raman-spectral-analysis-serotonin

Machine Learning-assisted Raman Spectral Analysis of Serotonin-responsive ssDNA-SWCNT Nanosensor for Improved Selectivity against Dopamine

Serotonin (5-hydroxytryptamine, 5-HT) plays critical roles in neuromodulation, yet current detection methods struggle to provide real-time sensing of 5-HT ...

Pukyong National University

The desire to enhance the efficiency of organic light-emitting devices (OLEDs) has driven to the investigation of advanced materials with fascinating properties. In this work, the efficiency of top-emission OLEDs (TEOLEDs) is enhanced by introducing ampicillin microstructures (Amp-MSs) with dual phases (α-/β-phase) that induce photoluminescence (PL) and electroluminescence (EL). Moreover, Amp-MSs can adjust the charge balance by Fermi level (E ) alignment, thereby decreasing the leakage current. The decrease in the wave-guided modes can enhance the light outcoupling through optical scattering. The resulting TEOLED demonstrates a record-high external quantum efficiency (EQE) (maximum: 68.7% and average: 63.4% at spectroradiometer; maximum: 44.8% and average: 42.6% at integrating sphere) with a wider color gamut (118%) owing to the redshift of the spectrum by J-aggregation. Deconvolution of the EL intensities is performed to clarify the contribution of Amp-MSs to the device EQE enhancement (optical scattering by Amp-MSs: 17.0%, PL by radiative energy transfer: 9.1%, and EL by J-aggregated excitons: 4.6%). The proposed TEOLED outperforms the existing frameworks in terms of device efficiency.

Efficient Photon Extraction in Top-Emission Organic Light-Emitting Devices Based on Ampicillin Microstructures.

Organic-inorganic hybrid perovskite nanoparticles (OIHP NPs) have attracted scientific attention owing to their efficient photoluminescence with optical tunability, which is highly advantageous for optoelectronic applications. However, the limited long-term stability of OIHP NPs has significantly hindered their practical application. Despite several synthetic strategies and encapsulation methods to stabilize OIHP NPs, complicated multi-step procedures are often required. In this study, we introduce an in situ ligand engineering method for stabilizing and controlling the optical properties of OIHP NPs using tetraalkylammonium (TAA) halides with various molecular structures at different concentrations. Our one-pot ligand engineering substantially enhanced the stability of the OIHP NPs without post-synthetic processes. Moreover, in certain cases, approximately 90% of the initial photoluminescence (PL) intensity was preserved even after a month under ambient conditions (room temperature, 20-50% relative humidity). To determine the role of ligand engineering in stabilizing the OIHP NPs, the surface binding properties of the TAA ligands were thoroughly analyzed using Raman spectroscopy. Specifically, the permanent positive charge of the TAA cations and consequent effective electrostatic interactions with the surfaces of the OIHP NPs are pivotal for preserving the initial PL intensity. Our investigation is beneficial for developing OIHP nanomaterials with improved stability and controlled photoluminescence for various optoelectronic applications, such as light-emitting devices, photosensitizers, photodetectors, photocatalysis, and solar cells.

In Situ Tetraalkylammonium Ligand Engineering of Organic-Inorganic Hybrid Perovskite Nanoparticles for Enhancing Long-Term Stability and Optical Tunability.

In this study, to obtain high performances of the dye-sensitized solar cells using the optimal TiO photoelectrode for the synthesized pyrazine-based organic photosensitizers, three types of TiO photoelectrodes were fabricated and evaluated for comparison. The double-layered nanoporous TiO photoelectrode (SPD type) consisted of a dispersed TiO layer and a transparent TiO layer. The single-layered nanoporous TiO photoelectrodes (D type and SP type) consisted of a dispersed TiO layer and a transparent TiO layer, respectively. The surface area, pore volume, and crystalline structures of the three types of TiO photoelectrodes were analyzed by Brunauer-Emmett-Teller method, field-emission scanning electron microscopy, and X-ray diffractometry to confirm their crystallinity and surface morphology. The structures of the three types of TiO photoelectrode-adsorbed organic sensitizers were investigated using X-ray photoelectron spectroscopy. The photovoltaic performances of DSSC devices using three organic photosensitizers adsorbed onto the three types of TiO photoelectrodes were investigated under a light intensity of 100 mW/cm at AM 1.5. The DSSC device using double-layered SPD type TiO photoelectrodes displayed 1.31∼2.64% efficiency, compared to single-layered SP type TiO photoelectrodes (1.31∼2.50%) and D type TiO photoelectrodes (0.90∼1.54%), using organic photosensitizers. The DSSC device using the SPD type TiO photoelectrode and trifluoromethylbenzopyrazine (TPPF) as a photosensitizer showed the highest performances:   of 5.69 mA/cm,   of 0.69 V,  of 0.67, and efficiency of 2.64%. The relationship between photovoltaic effects and interfacial resistance characteristics of DSSCs using the three organic photosensitizers adsorbed onto the three types of TiO photoelectrodes could be interpreted from interfacial resistances according to frequency through impedance analysis.

Photovoltaic Effects of Dye-Sensitized Solar Cells Using Double-Layered TiO Photoelectrodes and Pyrazine-Based Photosensitizers.

The development of heavy-atom-free photosensitizers (PSs) for photodynamic therapy (PDT) has encountered significant challenges in achieving simultaneous high fluorescence emission and reactive oxygen species (ROS) generation. Moreover, the limited water solubility of these PSs imposes further limitations on their biomedical applications. To overcome these obstacles, this study presents a molecular design strategy employing hydrophilic heavy-atom-free PSs based on imidazolium salts. The photophysical properties of these PSs were comprehensively investigated through a combination of experimental and theoretical analyses. Notably, among the synthesized PSs, the ethylcarbazole-naphthoimidazolium () conjugate exhibited efficient fluorescence emission (Φ = 0.22) and generation of singlet oxygen (Φ = 0.49), even in highly aqueous environments. The performance of  was validated through its application in fluorescence bioimaging and PDT treatment in HeLa cells. Furthermore,  holds promise for two-photon excitation and type I ROS generation, nucleus localization, and selective activity against Gram-positive bacteria, thereby expanding its scope for the design of heavy-atom-free PSs and phototheranostic applications.

Imidazolium-Based Heavy-Atom-Free Photosensitizer for Nucleus-Targeted Fluorescence Bioimaging and Photodynamic Therapy.

Cancer has emerged as a significant global health challenge, ranking as the second leading cause of death worldwide. Moreover, cancer patients frequently experience compromised immune systems, rendering them susceptible to bacterial infections. Combining anticancer and antibacterial properties in a single drug could lead to improved overall treatment outcomes and patient well-being. In this context, the present study focused on a series of hydrophilic naphthoimidazolium salts with donor groups (NI-R), aiming to create dual-functional agents with antibacterial and anticancer activities. Among these compounds, NI-TPA demonstrated notable antibacterial activity, particularly against drug-resistant bacteria, with MIC value of 7.8 μg mL. Furthermore, NI-TPA exhibited the most potent cytotoxicity against four different cancer cell lines, with an IC range of 0.67-2.01 μg mL. The observed high cytotoxicity of NI-TPA agreed with molecular docking and dynamic simulation studies targeting c-Met kinase protein. Additionally, NI-TPA stood out as the most promising candidate for two-photo excitation, fluorescence bioimaging, and localization in lysosomes. The study findings open new avenues for the design and development of imidazolium salts that could be employed in phototheranostic applications for cancer treatment and bacterial infections.

Dual anticancer and antibacterial activity of fluorescent naphthoimidazolium salts.

This study entailed the synthesis of Ru nanocatalyst decorated on Nb-grafted SBA-15. A Nb-grafted SBA-15 support with varying Nb contents was utilized as a support for the Ru nanoparticles. The effect of Nb grafting on the immobilized Ru nanoparticle catalyst was systematically investigated, and its catalytic performance in the synthesis of furandicarboxylic acid using 5-hydroxymethylfurfural under base-free reaction conditions was evaluated. The results indicate the increased productivity of the Ru@Nb-grafted SBA-15 catalyst with a yield exceeding 95%, representing a significant advancement in catalysis. This study also affords insights into the complex relationship between the catalytic activity and selectivity and its unique surface attributes. Moreover, acidic sites were created, and the electron density within the active sites was modulated by monomeric Nb oxide species on the SBA-15. Additionally, the role of high-electron-density Ru atoms in facilitating the efficient adsorption and activation of the reactant, resulting in enhanced catalytic efficacy, was highlighted.

Synergistic Interaction between Ruthenium Catalysts and Grafted Niobium on SBA-15 for 2,5-Furandicarboxylic Acid Production Using 5-Hydroxymethylfurfural.

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films have emerged as potential alternatives to indium-tin oxide as transparent electrodes in optoelectronic devices because of their superior transparency, flexibility, and chemical doping stability. However, pristine PEDOT:PSS films show low conductivities because the insulating PSS-rich domains isolate the conductive PEDOT-rich domains. In this study, the conductivities and corresponding spatially resolved Raman properties of PEDOT:PSS thin films treated with various concentrations of HSO are presented. After the PEDOT:PSS films are treated with the HSO solutions, their electrical conductivities are significantly improved from 0.5 (nontreated) to 4358 S cm (100% v/v). Raman heat maps of the peak shifts and widths of the C═C stretching mode are constructed. A blueshift and width decrease of the C═C Raman mode in PEDOT are uniformly observed in the entire measurement area (20 × 20 µm), indicating that microstructural transitions are successfully accomplished across the area from the coiled to linear conformation and high crystallinity upon HSO treatment. Thus, it is proved that comprehensive Raman map analysis can be easily utilized to clarify microstructural properties distributed in large areas induced by various dopants. These results also offer valuable insights for evaluating and optimizing the performance of other conductive thin films.

Enhanced Microstructural Uniformity in Sulfuric-Acid-Treated Poly(3,4-Ethylenedioxythiophene):Poly(Styrene Sulfonate) Films Using Raman Map Analysis.

This study compared the photoluminescence (PL) stabilities of formamidinium (FA) and methylammonium (MA) in lead iodide perovskite quantum dots (QDs). To exclude other factors, such as size and purity, that may affect stability, MAPbI and FAPbI QDs with nearly identical sizes (~10.0 nm) were synthesized by controlling the ligand concentration and synthesis temperature. Transmission electron microscopy images and X-ray diffraction patterns confirmed homogeneous single-phase perovskite structures. Additionally, the bandgaps and sizes of the synthesized QDs closely matched those of the infinite quantum well model, which guaranteed that the photostability was solely caused by the different organic molecules in the two QDs. We analyzed the PL peak centers and full-width at half maximum of the QDs for 32 days. The enhanced stability of FAPbI was found to be caused by the nearly zero redshift (1.615 eV) of its PL peak, in contrast to the redshift (1.685→1.670 eV) of MAPbI.

Long-Term Comparisons of Photoluminescence Affected by Organic Cations of Formamidinium and Methylammonium in Monophasic Lead Iodide Perovskite Quantum Dots.

The photophysical properties of methylammonium lead iodide (MAPbI) quantum dots (QDs) have not been systematically studied for size and shape dependence. Here, we synthesize MAPbI QDs using ligand-assisted reprecipitation, controlling the injection speed and reaction times to produce QDs with different sizes and shapes. Dropwise injection yields ∼5 nm spherical QDs, emitting photoluminescence (PL) at 2.06 eV. In contrast, swift injections yield larger (>10 nm) rectangular QDs with varying aspect ratios, supported by an infinite quantum well model. The PL lifetime of QDs increases with their size, and the size variation significantly influences the ultra-low-frequency Raman modes at 81, 107, and 127 cm, in contrast to what is observed in polymorphic MAPbI thin films. Our findings, supported by first-principles density functional theory, show that key PL and Raman properties are governed by the sizes and shapes of MAPbI QDs. This study contributes to the understanding of the optical behavior of these QDs, which is crucial for their potential applications and environmental implications.

Role of Size and Shape in Photoluminescence and Ultra-Low-Frequency Raman of Methylammonium Lead Iodide Perovskite Quantum Dots.

In this study, we developed a label-free biosensor based on aptamer-modified multi-walled carbon nanotube extended gate field-effect transistor (MWCNT-EG-FET) for easy and selective detection of microcystin-LR (MC-LR), a prominent cyanotoxin associated with liver damage, bleeding, and necrosis. EG-FET had two parts: a MOSFET and an extended-gate Au/SiO electrode, which serves as the sensitive membrane. A custom-designed DNA oligonucleotide (5-NH-C-AN6) was used as MC-LR-targeting aptamer (MCTA). MWCNTs were functionalized with MCTA and then stably fixed on the sensitive membrane. The detection of MC-LR in freshwater was effectively achieved within 5 min by assessing the variations in electrical resistance that occur due to the selective interactions between MC-LR and MCTA. The detection limit and analytical sensitivity of the biosensor for MC-LR were found to be 0.134 ng/mL and 0.024 ng/mL, respectively. The sensitive membrane could be readily discarded if damaged, eliminating the need to replace the main transducer MOSFET. The developed sensor exhibits features such as straightforward preparation, swift response, potential for miniaturization, and ease of use, making it an attractive candidate for future integrated lab-on-chip systems for MC-LR detection in freshwater environments.

Label-Free Extended Gate Field-Effect Transistor for Sensing Microcystin-LR in Freshwater Samples.

Stretchable devices have attracted significant attention due to their mechanical versatility and potential applications in wearable electronics, soft robotics, and biomedical devices. However, their practical implementation is often hindered by challenges in surface engineering, particularly at the interface between stretchable elastomers and conducting polymers like poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). This study introduces a novel strategy to enhance the performance of stretchable devices by engineering the elastomer substrate surface with 2,6-diaminopimelic acid (DAP), an amino-functionalization approach that improves integration with lab-synthesized PEDOT:PSS. DAP, a key diamino dicarboxylic acid component of Gram-negative bacterial cell wall peptidoglycan, is employed to facilitate amino and hydroxyl group activation on the elastomer surface. This process consequently improves the adhesion, mechanical stability, surface energy, and electrical conductivity at the interface between the elastomer and PEDOT:PSS. The electrical properties of the modified films were assessed under various mechanical deformations, demonstrating enhanced conductivity and stability. Chemical analyses using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) revealed that DAP functions as an interfacial bridge, forming chemical bonds or complexes between the elastomer surface and the functional groups in PEDOT:PSS. Increased adhesivity was confirmed by a lower contact angle and an improved adhesion energy of 134.4 mN/m. In conclusion, DAP-based surface modification is a promising approach for improving the key properties of stretchable devices. These findings support the development of robust electronics, including wearable heaters and alternating current electroluminescent (ACEL) devices, for broader applications in stretchable technologies.

Article	Year
Efficient Photon Extraction in Top-Emission Organic Light-Emitting Devices Based on Ampicillin Microstructures. Advanced materials (Deerfield Beach, Fla.)\| PubMed ID: 35700272	2022
In Situ Tetraalkylammonium Ligand Engineering of Organic-Inorganic Hybrid Perovskite Nanoparticles for Enhancing Long-Term Stability and Optical Tunability. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 36288550	2022
Photovoltaic Effects of Dye-Sensitized Solar Cells Using Double-Layered TiO Photoelectrodes and Pyrazine-Based Photosensitizers. ACS omega\| PubMed ID: 37125135	2023
Imidazolium-Based Heavy-Atom-Free Photosensitizer for Nucleus-Targeted Fluorescence Bioimaging and Photodynamic Therapy. ACS applied materials & interfaces\| PubMed ID: 37812505	2023
Dual anticancer and antibacterial activity of fluorescent naphthoimidazolium salts. RSC advances\| PubMed ID: 38099251	2023
Synergistic Interaction between Ruthenium Catalysts and Grafted Niobium on SBA-15 for 2,5-Furandicarboxylic Acid Production Using 5-Hydroxymethylfurfural. ACS applied materials & interfaces\| PubMed ID: 38315818	2024
Enhanced Microstructural Uniformity in Sulfuric-Acid-Treated Poly(3,4-Ethylenedioxythiophene):Poly(Styrene Sulfonate) Films Using Raman Map Analysis. Macromolecular rapid communications\| PubMed ID: 38850109	2024
Long-Term Comparisons of Photoluminescence Affected by Organic Cations of Formamidinium and Methylammonium in Monophasic Lead Iodide Perovskite Quantum Dots. Chemistry, an Asian journal\| PubMed ID: 38898704	2024
Role of Size and Shape in Photoluminescence and Ultra-Low-Frequency Raman of Methylammonium Lead Iodide Perovskite Quantum Dots. The journal of physical chemistry letters\| PubMed ID: 39899795	2025
Label-Free Extended Gate Field-Effect Transistor for Sensing Microcystin-LR in Freshwater Samples. Sensors (Basel, Switzerland)\| PubMed ID: 40096432	2025
Amino-Functionalized Surface Engineering of Elastomers for Robust PEDOT:PSS-Based Stretchable Electronics. ACS applied materials & interfaces\| PubMed ID: 41383144	2025

Myeongkee Park

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