Spectroscopy of an intrinsic fluorophore in animal and plant milk for potential identification of their quality.

Riboflavin (RF), commonly known as vitamin B2, is an essential ingredient in any milk variety of animal origin. The photophysics of the molecule RF, including its interaction with biological macromolecules, are well studied. Here, we have investigated the possibility of the molecule as a potential biomarker of milk quality. We also found omnipresence of this molecule in milk of plant origin (soy milk). Spectroscopic studies on various animal and plant milks of different commercial origins confirmed the potential of RF for use in identifying the quality of the milk varieties. Our developed strategy involved identification or spectroscopic signature of RF by measuring optical density at 365 nm (quality factor 1) and fluorescence intensity around 520 nm (excitation at 365 nm; quality factor 2) on a very small amount of whole milk (10 µL). We also developed a prototype device called Mil-Q-Way to be used in the real field. The required interfacing software in the LabView platform was also developed. A 2-parameter plot (quality factor 1 on the x-axis and quality factor 2 on the y-axis) called the Mil-Q-Way plot clearly differentiates the quality of milks of different commercial origins. The low-cost device based on simple spectroscopy was shown to screen for the presence of harmful adulterants in drinkable milk.

Exciton dissociation in an NIR-active triohybrid nanocrystal leading to efficient generation of reactive oxygen species.

Lead sulfide (PbS) colloidal quantum dots (QDs) are emerging materials for fundamental studies because of their potential application in near infrared (NIR) light harvesting technologies. However, inefficient electron separation, facile charge recombination and defect state trapping of photoexcited carriers are reported as limitations of the PbS QDs to achieve efficient energy conversion. In the present study, we have synthesized a triohybrid by assembling a semiconductor titanium dioxide (TiO2), an organic oxidizing molecule phenothiazine (PTZ) and PbS QDs. The triohybrid along with PbS_TiO2 and PbS_PTZ hybrids has been characterized and the attachment of different components is verified by spectroscopic and microscopic techniques. The interfacial dynamics of the photoexcited carriers in the PbS_TiO2 and PbS_PTZ hybrids have been investigated separately using steady state and time resolved photoluminescence (TRPL) measurements. The photoinduced electron transfer (PET) from the PbS QD to the conduction band (CB) of TiO2 and photoinduced hole transfer (PHT) from the valence band (VB) of the QD to the highest occupied molecular orbital (HOMO) of PTZ have been observed and correlated mechanistically to the energy level alignments obtained from cyclic voltammetric (CV) analysis. The PTZ molecule is also found to act as a surface defect passivator of the PbS QD. Finally, simultaneous exciton dissociation and reduced back recombination phenomena have been correlated with a higher reactive oxygen species (ROS) generation activity of the triohybrid than the other two, under IR light irradiation. Thus, a detailed investigation of carrier dynamics and the mechanism of higher NIR light activity for a novel nanohybrid is explored and analyzed which could be beneficial for NIR catalysis or antibacterial activities.

Ultrafast dynamics in co-sensitized photocatalysts under visible and NIR light irradiation.

Co-sensitization to achieve a broad absorption window is a widely accepted technique in light harvesting nanohybrid synthesis. Protoporphyrin (PPIX) and squaraine (SQ2) are two organic sensitizers absorbing in the visible and NIR wavelength regions of the solar spectrum, respectively. In the present study, we have sensitized zinc oxide (ZnO) nanoparticles using PPIX and SQ2 simultaneously for their potential use in broad-band solar light harvesting in photocatalysis. Förster resonance energy transfer (FRET) from PPIX to SQ2 in close proximity to the ZnO surface has been found to enhance visible light photocatalysis. In order to confirm the effect of intermolecular FRET in photocatalysis, the excited state lifetime of the energy donor dye PPIX has been modulated by inserting d10 (ZnII) and d7 (CoII) metal ions in the central position of the dye (PP(Zn) and PP(Co)). In the case of PP(Co)-SQ2, extensive photo-induced ligand to metal charge transfer counteracts the FRET efficiency while efficient FRET has been observed for the PP(Zn)-SQ2 pair. This observation has been justified by the comparison of the visible light photocatalysis of the respective nanohybrids with several control studies. We have also investigated the NIR photocatalysis of the co-sensitized nanohybrids which reveals that reduced aggregation of SQ2 due to co-sensitization of PPIX increases the NIR photocatalysis. However, core-metalation of PPIX reduces the NIR photocatalytic efficacy, most probably due to excited state charge transfer from SQ2 to the metal centre of PP(Co)/PP(Zn) through the conduction band of the host ZnO nanoparticles.

Femtosecond Electron-Transfer Dynamics across the D2O/Cs+/Cu(111) Interface: The Impact of Hydrogen Bonding.

Hydrogen bonding is essential in electron-transfer processes at water-electrode interfaces. We study the impact of the H-bonding of water as a solvent molecule on real-time electron-transfer dynamics across a Cs+-Cu(111) ion-metal interface using femtosecond time-resolved two-photon photoelectron spectroscopy. We distinguish in the formed water-alkali aggregates two regimes below and above two water molecules per ion. Upon crossing the boundary of these regimes, the lifetime of the excess electron localized transiently at the Cs+ ion increases from 40 to 60 fs, which indicates a reduced alkali-metal interaction. Furthermore, the energy transferred to a dynamic structural rearrangement due to hydration is reduced from 0.3 to 0.2 eV concomitantly. These effects are a consequence of H-bonding in the water-water interaction and the beginning formation of a nanoscale water network. This finding is supported by real-space imaging of the solvatomers and vibrational frequency shifts of the OH stretching and bending modes calculated for these specific interfaces.

Combating Essential Metal Toxicity: Key Information from Optical Spectroscopy.

Chelation therapy is one of the most effective and widely accepted methods of treatment to reduce metal toxicity caused by an excess amount of essential metals. Essential minerals play an important role in maintaining healthy human physiology. However, the presence of an excess amount of such essential metals can cause cell injury, which finally leads to severe life-threatening diseases. Chelating complexes can efficiently capture the targeted metal and can easily be excreted from the body. Commonly utilized metal chelators have major side effects including long-term damage to some organs, which has pointed out the need of less harmful biocompatible chelating agents. In this work, we have investigated the iron chelating property of curcumin through various spectroscopic tools by synthesizing and characterizing the iron-curcumin (Fe-Cur) complex. We have also investigated whether the synthesized materials are able to retain their antioxidant activity after the chelation of a substantial amount of metal ion. Our study unravels the improved antioxidant activity of the synthesized chelate complex. We further demonstrate that the proposed complex generates no significant reactive oxygen species (ROS) under dark conditions, which makes it a promising candidate for chelation therapy of iron toxicity. Femtosecond-resolved fluorescence studies further provide insight into the mechanism of activity of the new complex where electron transfer from ligand to metal has been observed prominently. Thus, the Fe-Cur complex has a potential to act as a dual activity medicine for excretion of toxic metal ions via chelation and as a therapeutic agent of oxidative stress caused by the metal ion as well.

In situ measurement of temperature dependent picosecond resolved carrier dynamics in near infrared (NIR) sensitive device on action.

The carrier dynamics study of emerging near infrared (NIR) absorbing materials is an essential need to develop device technology toward enhanced NIR light harvesting. In this study, we have documented the design of an indigenously developed time correlated single photoncounting (TCSPC) system working in the NIR (900 nm-1700 nm) spectral region. The system is compatible to study transient photoluminescence of device samples under tunable bias voltages. The liquid nitrogen cooling and electrical heating of the sample chamber provides additional flexibility of temperature dependent study starting from -196 °C to 400 °C. As a model system to study, we have chosen a multilayer InAs/InGaAs/GaAs/AlGaAs dot in the dual well device sample as the thin film quantum dot heterostructures are of huge relevance in various NIR harvesting devices. We have investigated the detail carrier dynamics of the device sample using the transient photoluminescence upon varying temperature (80 K-300 K), varying emission energy and different bias voltages (0 V-15 V). The critical temperature (160 K) and critical bias (12 V) of achieving longest excited state lifetime has been mechanistically explained using various competing photophysical phenomena such as hole diffusion, energy relaxation, etc. The emission wavelength dependent study at below and above critical temperature further provides an insight into the dominance of carrier capture and thermal escape at the two different temperature zones. Along with the detail understanding of the carrier dynamics, the results can be helpful to get an idea of the electrical stability of the device and the operability temperature as well. The reasonable good resolution of the NIR TCSPC system and considerable good results ensure the future application of the same for other devices also.

Complexation With Human Serum Albumin Facilitates Sustained Release of Morin From Polylactic-Co-Glycolic Acid Nanoparticles.

Understanding the interaction of proteins with nanoparticles has become an important area of research in biomedical and pharmaceutical fields. Morin is a flavonol which shows several properties including antioxidant, anticancer, and anti-inflammatory activities. However, the major limitation is its poor aqueous solubility. Therefore, morin-loaded polylactic-co-glycolic acid (PLGA) nanoparticles (MPNPs) were prepared to improve the solubility of morin. The resulting MPNPs were characterized by spectroscopic and microscopic techniques. The nanoparticles were spherical with an average size of 237 ± 17 nm. UV-visible, fluorescence, and circular dichroism (CD) spectroscopy were employed to study the interaction of the MPNPs with human serum albumin (HSA). Our study revealed that a static fluorescence quenching mechanism was involved in the interaction between HSA and MPNPs. Hydrophobic interactions also play an important role in stabilizing the HSA-MPNP complex. CD results suggest that there is an alteration of the secondary structure of HSA in the presence of MPNPs. MPNPs exhibit antioxidant properties which are supported by the DPPH assay. We have further checked the effect of HSA on the antioxidant property of morin and MPNPs. HSA binding with MPNPs was also found to influence the in vitro release property of morin from MPNPs wherein a delayed release response is observed.

Three-in-one approach towards efficient organic dye-sensitized solar cells: aggregation suppression, panchromatic absorption and resonance energy transfer.

In the present study, protoporphyrin IX (PPIX) and squarine (SQ2) have been used in a co-sensitized dye-sensitized solar cell (DSSC) to apply their high absorption coefficients in the visible and NIR region of the solar spectrum and to probe the possibility of Förster resonance energy transfer (FRET) between the two dyes. FRET from the donor PPIX to acceptor SQ2 was observed from detailed investigation of the excited-state photophysics of the dye mixture, using time-resolved fluorescence decay measurements. The electron transfer time scales from the dyes to TiO2 have also been characterized for each dye. The current-voltage (I-V) characteristics and the wavelength-dependent photocurrent measurements of the co-sensitized DSSCs reveal that FRET between the two dyes increase the photocurrent as well as the efficiency of the device. From the absorption spectra of the co-sensitized photoanodes, PPIX was observed to be efficiently acting as a co-adsorbent and to reduce the dye aggregation problem of SQ2. It has further been proven by a comparison of the device performance with a chenodeoxycholic acid (CDCA) added to a SQ2-sensitized DSSC. Apart from increasing the absorption window, the FRET-induced enhanced photocurrent and the anti-aggregating behavior of PPIX towards SQ2 are crucial points that improve the performance of the co-sensitized DSSC.