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1. Methylene Blue-Catalyzed Oxidative Cleavage of N-Carbonylated Indoles

   https://doi.org/10.1055/s-0036-1592006  

   Wu, Kui; Fang, Cheng; Kaur, Sarbjeet; Liu, Peng; Wang, Ting (July 2018, Synthesis)

   The development of a visible-light-mediated oxidative cleavage of electron-deficient indoles is reported. Methylene blue serves as an effective catalyst and the transformation shows a broad substrate scope. A variety of functional groups are well accommodated in the mild reaction conditions. The photo-mediated single electron transfer and oxidative cleavage mechanisms were investigated via density functional theory and Marcus theory calculations. 

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2. Voltage controlled bio-organic inverse phototransistor

   https://doi.org/10.1116/6.0001692  

   Mishra, Esha; Ekanayaka, Thilini K.; Dowben, Peter A. (March 2022, Biointerphases)

   Thin films of poly-d-lysine act as polar organic and are also light sensitive. The capacitance-voltage, current-voltage, and transistor behavior were studied to gauge the photoresponse of possible poly-d-lysine thin film devices both with and without methylene blue as an additive. Transistors fabricated from poly-d-lysine act as inverse phototransistors, i.e., the on-state current is greatest in the absence of illumination. The poly-d-lysine thin film capacitance and the transistor current decrease with illumination, both with and without methylene blue as an additive. This suggests that the unbinding of photo exciton is significantly hindered in this system which is supported by the significant charge carrier lifetime for poly-d-lysine films both with and without methylene blue. For the majority carrier, the transistor geometry appears to depend on the gate voltage; in other words, the majority carrier depends on the polarization of the poly-d-lysine films, both with and without methylene blue as an additive. 

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3. Self-assembled peptide-dye nanostructures for in vivo tumor imaging and photodynamic toxicity

   https://doi.org/10.1038/s44303-024-00008-4  

   Borum, Raina M.; Retout, Maurice; Creyer, Matthew N.; Chang, Yu-Ci; Gregorio, Karlo; Jokerst, Jesse V. (March 2024, npj Imaging)

   Abstract We report noncovalent assemblies of iRGD peptides and methylene blue dyes via electrostatic and hydrophobic stacking. These resulting nanomaterials could bind to cancer cells, image them with photoacoustic signal, and then treat them via photodynamic therapy. We first assessed the optical properties and physical properties of the materials. We then evaluated their utility for live cell targeting, in vivo imaging, and in vivo photodynamic toxicity. We tuned the performance of iRGD by adding aspartic acid (DD) or tryptophan doublets (WW) to the peptide to promote electrostatic or hydrophobic stacking with methylene blue, respectively. The iRGD-DD led to 150-nm branched nanoparticles, but iRGD-WW produced 200-nm nano spheres. The branched particles had an absorbance peak that was redshifted to 720 nm suitable for photoacoustic signal. The nanospheres had a peak at 680 nm similar to monomeric methylene blue. Upon continuous irradiation, the nanospheres and branched nanoparticles led to a 116.62% and 94.82% increase in reactive oxygen species in SKOV-3 cells relative to free methylene blue at isomolar concentrations suggesting photodynamic toxicity. Targeted uptake was validated via competitive inhibition. Finally, we used in vivo bioluminescent signal to monitor tumor burden and the effect of for photodynamic therapy: The nanospheres had little impact versus controls (p = 0.089), but the branched nanoparticles slowed SKOV-3 tumor burden by 75.9% (p < 0.05). 

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4. Anisotropic silica coating on gold nanorods boosts their potential as SERS sensors

   https://doi.org/10.1039/D1NR07918B  

   Meyer, Sean M.; Murphy, Catherine J. (March 2022, Nanoscale)

   Gold nanorods are well-known surface-enhanced Raman scattering substrates. Under longitudinal plasmonic excitation, the ends of the nanorods experience larger local electric fields compared to the sides of the rods, suggesting that Raman-active molecules would be best detected if the molecules could preferentially bind to the ends of the nanorods. Coating the tips of gold nanorods with anionic mesoporous silica caps enabled surface-enhanced Raman scattering (SERS) detection of the cationic dye methylene blue at lower concentrations than observed for the corresponding silica coating of the entire rod. By analyzing the intensity ratio of two Raman active modes of methylene blue and the surface plasmon resonance peak shift of the gold nanorod composites, it can be inferred that at a low concentration of methylene blue, molecules adsorb to the tips of the tip coated silica gold nanorods. Functionalization of the anionic silica endcaps with cationic groups eliminates the SERS enhancement for the cationic methylene blue, demonstrating the electrostatic nature of the adsorption process in this case. These results show that anisotropic silica coatings can concentrate analytes at the tips of gold nanorods for improvements in chemical sensing and diagnostics. 

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5. Multivariate Analysis on the Structure–Activity Parameters for Nano-CuOx-Catalyzed Reduction Reactions

   https://doi.org/10.1021/acsanm.3c04897  

   Shultz-Johnson, Lorianne R.; Chang, Matthew; Bisram, Neil N.; Bryant, Jacob T.; Martin, Christopher P.; Rahmani, Azina; Furst, Jacob I.; Caranto, Jonathan D.; Banerjee, Parag; Uribe-Romo, Fernando J.; et al (January 2024, ACS Applied Nano Materials)

   Understanding the origin of enhanced catalytic activity is critical to heterogeneous catalyst design. This is especially important for non-noble metal-based catalysts, notably metal oxides, which have recently emerged as viable candidates for numerous thermal catalytic processes. For thermal catalytic reduction/hydrogenation using metal oxide nanoparticles, enhanced catalytic performance is typically attributed to an increased surface area and the presence of oxygen vacancies. Concomitantly, the treatments that induce oxygen vacancies also impact other material properties, such as the microstrain, crystallinity, oxidation state, and particle shape. Herein, multivariate statistical analysis is used to disentangle the impact of material properties of CuO nanoparticles on catalytic rates for nitroaromatic and methylene blue reduction. The impact of the microstrain, shape, and Cu(0) atomic percent is demonstrated for these reactions; furthermore, a protocol for correlating material property parameters to catalytic efficiency is presented, and the importance of catalyst design for these broadly utilized probe reactions is highlighted. 

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