Immobilization of Glucose Oxidase on Glutathione Capped CdTe Quantum Dots for Bioenergy Generation

An efficient immobilization of Glucose oxidase (GOx) on an appropriate substrate is one of the main challenges of developing fuel cells that allow energy to be obtained from renewable substrates such as carbohydrates in physiological environments. The research importance of biofuel cells relies on their experimental robustness and high compatibility with biological organisms such as tissues or the bloodstream with the aim of obtaining electrical energy even from living systems. In this work, we report the use of 5,10,15,20 tetrakis (1-methyl-4-pyridinium) porphyrin and glutathione capped CdTe Quantum dots (GSH-CdTeQD) as a support matrix for the immobilization of GOx on carbon surfaces. Fluorescent GSH-CdTeQD particles were synthesized and their characterization by UV-Vis spectrophotometry showed a particle size between 5–7 nm, which was confirmed by DLS and TEM measurements. Graphite and Toray paper electrodes were modified by a drop coating of porphyrin, GSH-CdTeQD and GOx, and their electrochemical activity toward glucose oxidation was evaluated by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Additionally, GOx modified electrode activity was explored by scanning electrochemical microscopy, finding that near to 70% of the surface was covered with active enzyme. The modified electrodes showed a glucose sensitivity of 0.58 ± 0.01 μA/mM and an apparent Michaelis constant of 7.8 mM. The addition of BSA blocking protein maintained the current response of common interferent molecules such as ascorbic acid (AA) with less than a 5% of interference percentage. Finally, the complex electrodes were employed as anodes in a microfluidic biofuel cell (μBFC) in order to evaluate the performance in energy production. The enzymatic anodes used in the μBFC allowed us to obtain a current density of 7.53 mAcm−2 at the maximum power density of 2.30 mWcm−2; an open circuit potential of 0.57 V was observed in the biofuel cell. The results obtained suggest that the support matrix porphyrin and GSH-CdTeQD is appropriate to immobilize GOx while preserving the enzyme’s catalytic activity. The reported electrode arrangement is a viable option for bioenergy production and/or glucose quantification.

Hybrid Complexes of Photosensitizers with Luminescent Nanoparticles: Design of the Structure

Increasing the efficiency of the photodynamic action of the dyes used in photodynamic therapy is crucial in the field of modern biomedicine. There are two main approaches used to increase the efficiency of photosensitizers. The first one is targeted delivery to the object of photodynamic action, while the second one is increasing the absorption capacity of the molecule. Both approaches can be implemented by producing dye-nanoparticle conjugates. In this review, we focus on the features of the latter approach, when nanoparticles act as a light-harvesting agent and nonradiatively transfer the electronic excitation energy to a photosensitizer molecule. We will consider the hybrid photosensitizer-quantum dot complexes with energy transfer occurring according to the inductive-resonance mechanism as an example. The principle consisting in optimizing the design of hybrid complexes is proposed after an analysis of the published data; the parameters affecting the efficiency of energy transfer and the generation of reactive oxygen species in such systems are described.

Visual paper-based sensor for the highly sensitive detection of caffeine in food and biological matrix based on CdTe-nano ZnTPyP combined with chemometrics

Caffeine naturally occurs in tea and cocoa, which is also used as an additive in beverages and has pharmacological effects such as refreshing, antidepressant, and digestion promotion, but excessive caffeine can cause harm to the human body. In this work, based on the specific response between nano zinc 5, 10, 15, 20-tetra(4-pyridyl)-21H-23H-porphine (nano ZnTPyP)-CdTe quantum dots (QDs) and caffeine, combined with chemometrics, a visual paper-based sensor was constructed for rapid and on-site detection of caffeine. The fluorescence of QDs can be quenched by nano ZnTPyP. When caffeine is added to the system, it can pull nano ZnTPyP off the surface of the QDs to achieve fluorescence recovery through electrostatic attraction and nitrogen/zinc coordination. The detection range is 5 × 10^-11~3 × 10^-9 mol L^-1, and the detection limit is 1.53 × 10^-11 mol L^-1 (R² = 0.9990) (S/N = 3). The paper-based sensor constructed exhibits good results in real samples, such as tea water, cell culture fluid, newborn bovine serum, and human plasma. Therefore, the sensor is expected to be applied to the rapid instrument-free detection of caffeine in food and biological samples.Graphical abstract.

Enhancing Singlet Oxygen Generation in Conjugates of Silicon Nanocrystals and Organic Photosensitizers

Silicon nanocrystals (SiNCs) are regarded as a green and environmentally friendly material when compared with other semiconductor nanocrystals. Ultra-small SiNCs (with the size 4.6-5.2 nm) demonstrate strong UV absorption and photoluminescence in the near infrared (NIR) range with the high photoluminescence quantum yield (PLQY) up to 60%. In contrast to nanoporous silicon, ultra-small SiNCs do not possess an intrinsic ability to generate singlet oxygen (1O2). However, we demonstrate that SiNC-dye conjugates synthesized via microwave assistant hydrosilylation reaction produce 1O2 with moderate quantum yield (ΦΔ) up to 27% in cyclohexane. These interesting results were obtained via measurements of singlet oxygen phosphorescence at 1,270 nm. SiNCs play an important role in the production of singlet oxygen as SiNCs harvest UV and blue radiation and transfer absorbed energy to a triplet state of the attached dyes. It increases the population of the triplet states and leads to the enhancement of the singlet oxygen generation. Simultaneously, the SiNC-dye conjugates demonstrate NIR luminescence with the PLQY up to 22%. Thus, the luminescence behavior and photosensitizing properties of the SiNC-dye conjugates can attract interest as a new multifunctional platform in the field of bio-applications.

Modeling nonadiabatic dynamics in condensed matter materials: some recent advances and applications

This review focuses on recent developments in the field of nonadiabatic molecular dynamics (NA-MD), with particular attention given to condensed-matter systems. NA-MD simulations for small molecular systems can be performed using high-level electronic structure (ES) calculations, methods accounting for the quantization of nuclear motion, and using fewer approximations in the dynamical methodology itself. Modeling condensed-matter systems imposes many limitations on various aspects of NA-MD computations, requiring approximations at various levels of theory-from the ES, to the ways in which the coupling of electrons and nuclei are accounted for. Nonetheless, the approximate treatment of NA-MD in condensed-phase materials has gained a spin lately in many applied studies. A number of advancements of the methodology and computational tools have been undertaken, including general-purpose methods, as well as those tailored to nanoscale and condensed matter systems. This review summarizes such methodological and software developments, puts them into the broader context of existing approaches, and highlights some of the challenges that remain to be solved.

Strategies for extending charge separation in colloidal nanostructured quantum dot materials

Semiconductor colloidal metal chalcogenides (II-VI) in the form of quantum dots (QDs) and different heterostructures (core/shell, alloys, etc.) are of extensive interest in scientific research for both a fundamental understanding and technological applications because of their quantized size and different optical properties; however, due to their small size, the exciton (bound electron and hole) experiences a strong Coulombic attraction, which has a remarkable impact on the charge separation and photophysical properties of QDs. Thus, to achieve an efficient charge separation, numerous attempts have been made via the formation of different heterostructures, QD/molecular adsorbate (either organic or inorganic) assemblies, etc. These hybrid materials ameliorated the absorption of the incident light as well as charge separation. This article reviews the strategies for extending charge separation in these colloidal nanocrystals (NCs), which is one of the crucial steps to elevate the solar to electrical energy conversion efficiency in a quantum dot-sensitized solar cell (QDSC). The article summarizes the benefits of co-sensitization and experimental shreds of evidence for the multiple charge transfer processes involved in a QDSC. Studies have shown that in the co-sensitization process, prolonged charge separation occurs via the dual behavior of the molecular adsorbate, sensitization (electron injection) and capture of holes from photoexcited QDs. This perspective emphases band edge engineering and control of charge carrier dynamics in various core/shell structures. The impact of colloidal alloy NCs on charge separation and interesting photophysical properties was recapitulated via the steady-state and time-resolved photoluminescence (PL) and femtosecond transient absorption spectroscopic techniques. Finally, the prolonged lifetime and extent of charge separation for these hybrid NCs (or the composites) assisted in the development of a better light harvester as compared to the case of their pure counterparts.

Complexes between core-modified porphyrins ZnP(X)4 (X = P and S) and small semiconductor nanoparticle Zn6S6: are they possible?

The synthetic approach of the anchoring of porphyrins to the surface of semiconductor nanoparticles (NPs) has been realized to form very promising organic/inorganic nanocomposites. They have been of considerable scientific and a wide practical interest including such areas as material science, biomedical applications, and dye-sensitized solar cells (DSSCs). Macrocyclic pyrrole-containing compounds, such as phthalocyanines and porphyrins, can bind to the NP surface by a variety of modes: as monodentate ligands oriented perpendicular to the NP surface, parallel to the NP surface, or, alternatively, in a perpendicular orientation bridging two adjacent NPs. Also, non-covalent (coordination) interactions may be realized between the NP via its metal centers and appropriate meso-attached groups of porphyrins. Recently, we showed computationally that the prominent structural feature of the core-modified MP(X)4 porphyrins (X = P) is their significant distortion from planarity. Motivated by the phenomenon of numerous complexes formation between tetrapyrrols and NPs, we performed the density functional theory (DFT) studies of the complex formation between the core-modified ZnP(X)4 species (X = P and S) without any substituents or linkers and semiconductor NPs, exemplified by small NP Zn6S6. The complexes formation was investigated using the following theoretical approaches: (i) B3LYP/6-31G* and (ii) CAM-B3LYP/6-31G*, both in the gas phase and with implicit effects from C6H6 considered. The calculated binding energies of the complexes studied were found to be significant, varying from ca. 29 up to ca. 69 kcal/mol, depending on the complex and the approach employed.

High quantum yield and well-dispersed quantum dots luminescent composite through sodium carboxymethyl starch

It is a challenging task to prepare well-dispersed and highly luminescent quantum dots (QDs) powder and a new strategy is reported in this article. Sodium carboxymethyl starch (CMS-Na) was employed in this work to prepare the QDs-starch composite. Ultraviolet (UV) light shows that the blank starches had no fluorescence, while the QDs-starches were highly luminescent. Scanning electron microscopy (SEM) observation shows that the QDs-starch composite has the typical particle morphology with the diameter around 200 nm. Energy dispersive X-ray spectroscopy (EDX) results show that there are intensive tellurium (Te) and cadmium (Cd) element signals. Combined fluorescent lifetime and steady-state spectrometer show that the QDs-starch quantum yields (QYs) increase when the QDs loading increases from 1 × 10^-6 mol/g to 2 × 10^-6 mol/g, but when the loadings further increase, the QYs decrease slightly. For the red colour (λ_em  = 660 nm) QDs, the QYs can reach to as high as 28.2%, and for the other colour QDs they can also have the QYs above 22%. Time-resolved photobleaching experiments show that the fluorescent QDs-starch composite has a half-decay time of 40.23 s. These results indicate that the CMS-Na is a promising QDs dispersant to obtain high QY QD composites.

Hybrid nickel-free graphene/porphyrin rings for photodegradation of emerging pollutants in water

A novel hybrid photoactive material based on graphene foam (G) coupled with porphyrin-based polymers (Porph rings) was formulated by using a time-saving procedure to remove nickel from the final device. Specifically, Porph rings were spin coated onto the G platform with the double function of a visible-light photocatalyst and protective agent during nickel etching. The characterization of G-Porph rings was assessed by Scanning Electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). The novel material showed photocatalytic ability in degrading different classes of pollutants such as the herbicide 2,4 dichlorophenoxyacetic acid (2,4-D), polyethylene glycol (PEG) as an ingredient of care and health products, and also the methylene blue (MB) dye. UV-Vis spectroscopy, total organic carbon (TOC) and soft mass spectrometry techniques were used to monitor the photocatalytic process. The best performance in terms of photocatalytic efficiency was exhibited versus PEG and MB degradation. Furthermore, to determine the individual contribution of Reactive Oxygen Species (ROS) produced, free radical and hole scavenging tests were also carried out. Finally, a detailed map of the photocatalytic degradation mechanisms was proposed, reporting also the calculation of Porph rings' Highest Occupied Molecular Orbital (HOMO) and Lowest Occupied Molecular Orbital (LUMO) energy level values.

A novel hybrid photoactive material based on graphene foam (G) coupled with porphyrin-based polymers (Porph rings) was formulated by using a time-saving procedure to remove nickel from the final device.

A CdSe/ZnS quantum dot-based platform for the delivery of aluminum phthalocyanines to bacterial cells

Enhancement of optical properties of photosensitizers by additional light-harvesting antennas is promising for the improvement of the photodynamic therapy. However, large number of parameters determine interactions of nanoparticles and photosensitizers in complex and, thus the photodynamic efficacy of the hybrid structure. In order to achieve high efficiency of energetic coupling and photodynamic activity of such complexes it is important to know the location of the photosensitizer molecule on the nanoparticle, because it affects the spectral properties of the photosensitizer and the stability of the hybrid complex in vitro/in vivo. In this work complexes of polycationic aluminum phthalocyanines and CdSe/ZnS quantum dots were obtained. We used quantum dots which outer shell consists of polymer with carboxyl groups and provides water solubility and the negative charge of the nanoparticle. We found that phthalocyanine molecules could penetrate deeply into the polymer shell of quantum dot, leading thereby to significant changes in the spectral and photodynamic properties of phthalocyanines. We also showed that noncovalent interactions between phthalocyanine and quantum dot provide possibility for a release of the phthalocyanine from the hybrid complex and its binding to both Gram-positive and Gram-negative bacterial cells. Also, detailed characterization of the nanoparticle core and shell sizes was carried out.

Photochemical behavior of biosupramolecular assemblies of photosensitizers, cucurbit[n]urils and albumins

Biosupramolecular assemblies combining cucurbit[n]urils (CB[n]s) and proteins for the targeted delivery of drugs have the potential to improve the photoactivity of photosensitizers used in the photodynamic therapy of cancer. Understanding the complexity of these systems and how it affects the properties of photosensitizers is the focus of this work. We used acridine orange (AO⁺) as a model photosensitizer and compared it with methylene blue (MB⁺) and a cationic porphyrin (TMPyP⁴⁺). Encapsulation of the photosensitizers into CB[n]s (n = 7, 8) modified their photoactivity. In particular, for AO⁺, the photo-oxidation of HSA was enhanced in the presence of CB[7]; meanwhile it was decreased when included into CB[8]. Accordingly, peroxide generation and protein fragmentation were also increased when AO⁺ was encapsulated into CB[7]. The triplet excited state lifetimes of all the photosensitizers were lengthened by their encapsulation into CB[n]s, while the singlet oxygen quantum yield was enhanced only for AO⁺ and TMPyP⁴⁺, but it decreased for MB⁺. The results obtained in this work prompt the necessity of further investigating these kinds of hybrid assemblies as drug delivery systems because of their possible applications in biomedicine.

"On the Dot"-The Timing of Self-Assembled Growth to the Quantum Scale

Understanding the complex world of material growth and tunability has mystified the minds of material scientists and has been met with increasing efforts to close the gap between controllability and applicability. The reality of this journey is frustratingly tortuous but is being eased through better conceptual appreciation of metal crystalline frameworks that originate from shape and size dependent solvent responsive growth patterns. The quantum confinement of TiO₂ in the range of 0.8-2 nm has been synthetically challenging to achieve but lessons from biomineralization processes have enabled alternative routes to be explored via self-induced pre-nucleation events. In driving this concept, we have incorporated many of these key features integrating aspects of low temperature annealing at the interface of complex heterogeneous nucleation between hard and soft materials to arrest the biomimetic amorphous phase of TiO₂ to a tunable crystalline quantumized state. The stabilization of metastable states of quantum sized TiO₂ driven by kinetic and thermodynamic processes show hallmarks of biomineralized controlled events that suggest the inter-play between new pathways and interfacial energies that preferentially favor low dimensionality at the quantum scale. This provides the potential to re-direct synthetic assemblies under tightly controlled parameters to generate a host of new materials with size, shape and anisotropic properties as smart stimuli responsive materials. These new stabilities leading to the growth arrest of TiO₂ are discussed in terms of molecular interactions and structural frameworks that were previously inaccessible via conventional routes. There exists an undiscovered parallel between synthetic and biomineralized routes enabling unprecedented access to the availability and tunability of novel quantum confined materials. The parametrics of complex material design at the crossroads of synthetically and biologically driven processes is only now surfacing.

Shape-Tunable Charge Carrier Dynamics at the Interfaces between Perovskite Nanocrystals and Molecular Acceptors

Hybrid organic/inorganic perovskites have recently emerged as an important class of materials and have exhibited remarkable performance in photovoltaics. To further improve their device efficiency, an insightful understanding of the interfacial charge transfer (CT) process is required. Here, we report the first direct experimental observation of the tremendous effect that the shape of perovskite nanocrystals (NCs) has on interfacial CT in the presence of a molecular acceptor. A dramatic change in CT dynamics at the interfaces of three different NC shapes, spheres, platelets, and cubes, is recorded. Our results clearly demonstrate that the mechanism of CT is significantly affected by the NC shape. More importantly, the results demonstrate that complexation on the NC surface acts as an additional driving force not only to tune the CT dynamics but also to control the reaction mechanism at the interface. This observation opens a new venue for further developing perovskite NCs-based applications.

A srikaya-like light-harvesting antenna based on graphene quantum dots and porphyrin unimolecular micelles

A novel hybrid light-harvesting antenna with a srikaya-like structure of multi-graphene quantum dots (GQDs) as donors and one porphyrin unimolecular micelle as the acceptor was constructed through electrostatic self-assembly.