Insights into the Mechanism of Quantum Dot-Sensitized Singlet Oxygen Production for Photodynamic Therapy

Nann T.

This article contains a critical review on the application of different types of nanoparticles in photodynamic therapy (PDT).Passive carrier particles like photosensitiser-"doped" silica nanoparticles are discussed as well as luminescent and noble metal nanocrystals in conjunction with molecular photosensitisers.Recent achievements are highlighted and the fundamental limitations of these systems are discussed.The article is concluded by an outlook on potential improvements and the possibility for practical applications of nanoparticle-based PDT.

Stuchinskaya T., Moreno M., Cook M.J., Edwards D.R., Russell D.A.

A 4-component antibody-phthalocyanine-polyethylene glycol-gold nanoparticle conjugate is described for use as a potential drug for targeted photodynamic cancer therapy. Gold nanoparticles (4 nm) were stabilised with a self-assembled layer of a zinc-phthalocyanine derivative (photosensitiser) and a heterobifunctional polyethylene glycol. Anti-HER2 monoclonal antibodies were covalently bound to the nanoparticles via a terminal carboxy moiety on the polyethylene glycol. The nanoparticle conjugates were stable towards aggregation, and under irradiation with visible red light efficiently produced cytotoxic singlet oxygen. Cellular experiments demonstrated that the nanoparticle conjugates selectively target breast cancer cells that overexpress the HER2 epidermal growth factor cell surface receptor, and that they are effective photodynamic therapy agents.

Moeno S., Antunes E., Nyokong T.

This work reports on the synthesis of several novel water soluble metallophthalocyanines containing Zn2+, In3+, Ga3+ or Si4+ as central metal ions and tetra substituted with mercaptoacetic acid and mercaptopropionic acid. The complexes were characterized using infra red, nuclear magnetic resonance and mass spectroscopies as well as elemental analysis. All the complexes are water soluble but the majority are highly aggregated in water and organic solvents. The complex containing Zn as a central metal and mercaptopropionic acid as a substituent was not aggregated allowing for the determination of photophysical parameters. This complex had triplet state quantum yield of 0.61 in DMF and 0.88 in DMSO while the fluorescence quantum yield was 0.13 in DMSO. The determination of photophysical properties of the complex containing Zn as a central metal and mercaptopropionic acid were carried out in the presence of mercaptopropionic acid capped CdTe quantum dots. There is an increase in triplet state quantum yield from 0.88 (for the phthalocyanine alone) to 0.94 (in the presence of CdTe quantum dots) in DMSO.

Wang D., Nap R.J., Lagzi I., Kowalczyk B., Han S., Grzybowski B.A., Szleifer I.

Dissociation of ionizable ligands immobilized on nanopaticles (NPs) depends on and can be regulated by the curvature of these particles as well as the size and the concentration of counterions. The apparent acid dissociation constant (pKa) of the NP-immobilized ligands lies between that of free ligands and ligands self-assembled on a flat surface. This phenomenon is explicitly rationalized by a theoretical model that accounts fully for the molecular details (size, shape, conformation, and charge distribution) of both the NPs and the counterions.

Duong H.D., Rhee J.I.

The singlet oxygen produced by the activation of the PpIX molecule was significantly enhanced through the FRET process from negatively and positively charged QDs with emission wavelengths of 550 nm and 580 nm, respectively, to the PpIX molecules. The activation of the QDs using LEDs at 410 nm and 470 nm, significantly contributed to the FRET process, as well as to the production of singlet oxygen. The singlet oxygen produced by the QDs and PpIX in this work could be used in the treatment of Escherichia coli . The entrapment of the QDs and PpIX into the sol–gel matrix GA produced sol–gel membranes with high efficiency of singlet oxygen production.

Wen Y.

Steady-state and nanosecond time-resolved spectroscopies are performed to investigate the interaction between CdSe quantum dots (QDs) and mesotetraphenylporphyrin (TPP) photosensitizers under two-photon excitation with 800-nm femtosecond laser pulses. The luminescent intensity and lifetime of the QDs decrease intensively in the QD-porphyrin mixture, whereas those of the TPP increase, suggesting occurence of a nonradiative fluorescence resonance energy transfer (FRET) process between the excited states of the donors and acceptors. An energy transfer efficiency of 0.27 is estimated from quenching of the excited-state radiative lifetime of the QDs. A 4-nm red shift in the emission spectrum of the CdSe QDs is observed after mixing with TPP, which is speculated to be caused by the energy transfer from QDs of small size to large. This study could be valuable for developing a QD-based drug system for application in two-photon excitation photodynamic therapy.

Sadhu S., Haldar K.K., Patra A.

In the present study, we demonstrate the size dependent resonance energy transfer from CdSe QDs (donor) to Nile Red dye (acceptor) using steady state and time-resolved spectroscopy. A strong eviden...

Rakovich A., Savateeva D., Rakovich T., Donegan J.F., Rakovich Y.P., Kelly V., Lesnyak V., Eychmüller A.

We have studied the photodynamic properties of novel CdTe quantum dots—methylene blue hybrid photosensitizer. Absorption spectroscopy, photoluminescence spectroscopy, and fluorescence lifetime imaging of this system reveal efficient charge transfer between nanocrystals and the methylene blue dye. Near-infrared photoluminescence measurements provide evidence for an increased efficiency of singlet oxygen production by the methylene blue dye. In vitro studies on the growth of HepG2 and HeLa cancerous cells were also performed, they point toward an improvement in the cell kill efficiency for the methylene blue-semiconductor nanocrystals hybrid system.

Leontowich A.F., Calver C.F., Dasog M., Scott R.W.

We report the synthesis of water-soluble, nearly monodisperse glycine-cysteamine (Gly-CSA) gold monolayer protected clusters (MPCs) via base deprotection of Fmoc-Gly-CSA MPCs. The resulting Gly-CSA MPCs, which have terminal primary amine groups, are fully characterized by (1)H and (13)C NMR, UV-vis spectroscopy, and TEM, and their surface properties were probed by dynamic light scattering and acid-base titrations. The characterization methods indicate that the as-synthesized particles are nearly monodisperse with an average particle size of 1.8 +/- 0.3 nm, but are only stable to aggregation in water at pHs of 4 and below. Acid-base titrations of the Gly-CSA MPCs show that the primary ammonium groups have a pK(a) of approximately 5.5, which is several orders of magnitude lower than the pK(a2) for the ammonium group of glycine (9.6). Thus, the particles are only partially protonated at intermediate pH's, which then drives the aggregation of the nanoparticles via hydrogen-bond formation. Dynamic light scattering results confirm the pH-driven aggregation of the nanoparticles, and studies with ninhydrin confirm that the primary amine groups are reactive and have potential for further functionalization. These results show that amine-terminated MPCs can be synthesized; however, their aggregation at intermediate pH's can limit their utility as building blocks for multifunctional nanoparticle syntheses.

Resch-Genger U., Grabolle M., Cavaliere-Jaricot S., Nitschke R., Nann T.

Suitable labels are at the core of luminescence and fluorescence imaging and sensing. One of the most exciting, yet also controversial, advances in label technology is the emerging development of quantum dots (QDs)—inorganic nanocrystals with unique optical and chemical properties but complicated surface chemistry—as in vitro and in vivo fluorophores. Here we compare and evaluate the differences in physicochemical properties of common fluorescent labels, focusing on traditional organic dyes and QDs. Our aim is to provide a better understanding of the advantages and limitations of both classes of chromophores, to facilitate label choice and to address future challenges in the rational design and manipulation of QD labels.

Xu S., Ziegler J., Nann T.

We report a simple method for the fast synthesis of highly photoluminescent InP and InP/ZnS core–shell nanocrystals (NCs) covering a wide range of emissions from blue to the near infrared. Both InP and InP/ZnS NCs were prepared in one-step, in a one-pot reaction within 20 min using an InCl3 complex as a precursor and zinc carboxylate as an initiator and stabilizer. The quantum yields of the InP and InP/ZnS NCs were 30% and 60%, respectively. This new synthetic method allows fast and reproducible preparation of InP and InP/ZnS NCs with a quality comparable to that of the frequently used CdSe-based ones. It is anticipated that these particles can be used to replace CdSe for many applications.

Ma J., Chen J., Idowu M., Nyokong T.

Singlet oxygen (1O2), one of the reactive oxygen species, plays an important role in many biomedical applications. The various compounds including the phthalocyanines, quantum dots (QDs) and QD complex, which may have potential to produce 1O2, thus received more and more attentions in recent years. By means of the direct detection of near-infrared 1270 nm, we found that the water-soluble thiol-capped CdTe QDs can photoproduce 1O2 in deuterated water with a low quantum yield (QY) of 1%. When sulfonated aluminum phthalocyanines (AlSPc's) were connected to these QDs, forming water-soluble QD-Pc composites, the 1O2 QY of the composites increased to 15% under the excitation of 532 nm, while little 1O2 production can be found for AlSPc alone at the same excitation because of the poor absorption of AlSPc in this region. The results of indirect measurements of 1O2, obtained from the photodegradation of the 1O2 chemical trap anthracene-9,10-diyl-bis-methylmalonate (ADMA), confirmed 1O2 yields in both QD and QD-Pc composite solutions. The QD-Pc composites have the advantage of extending the excitation region to 400-600 nm with remarkably enhanced extinction coefficients as compared with that of AlSPc. Therefore QD-Pc composites can fully utilize visible region light excitation to effectively produce 1O2, which may facilitate the applications of QD-Pc composites in broad areas.

Jana N.R., Earhart C., Ying J.Y.

Synthetic methods for high-quality near-monodispersed nanoparticles of metals, metal oxides, and quantum dots in organic solvents are well-developed, but their applications are restricted due to the lack of water solubility and tailored surface chemistry. In this work, we report the silica-coating procedure for various hydrophobic nanoparticles, including Au, Ag, Fe3O4, and ZnS−CdSe to derive water-soluble and functionalized nanoparticles. We have developed a silica-coating method in toluene using commercially available silanes. This approach is applicable to hydrophobic nanoparticles in the size range of 2−20 nm. Silica-coated nanoparticles are 10−30 nm in size, water-soluble, buffer-stable, and have a positive or negative surface charge depending on the surface functional group and solution pH. The coated particles have primary amine groups on the outer surface and are further functionalized with biotin and antibody.

Tsay J.M., Trzoss M., Shi L., Kong X., Selke M., Jung M.E., Weiss S.

Peptide-coated quantum dot-photosensitizer conjugates were developed using novel covalent conjugation strategies on peptides which overcoat quantum dots (QDs). Rose bengal and chlorin e6, photosensitizers (PSs) that generate singlet oxygen in high yield, were covalently attached to phytochelatin-related peptides. The photosensitizer-peptide conjugates were subsequently used to overcoat green- and red-emitting CdSe/CdS/ZnS nanocrystals. Generation of singlet oxygen could be achieved via indirect excitation through Förster (fluorescence) resonance energy transfer (FRET) from the nanocrystals to PSs, or by direct excitation of the PSs. In the latter case, by using two color excitations, the conjugate could be simultaneously used for fluorescence imaging and singlet oxygen generation. Singlet oxygen quantum yields as high as 0.31 were achieved using 532-nm excitation wavelengths.

Amao Y., Yamada Y.

Photovoltaic conversion using zinc chlorin-e6 (ZnChl-e6), which is zinc chlorophyll-a derivative, and fatty acid (myristic acid or cholic acid) co-adsorbed nanocrystalline TiO2 layer onto ITO glass (OTE) electrode is developed. The maximum peaks of photocurrent action spectrum of the ZnChl-e6 adsorbed TiO2 layer onto OTE (ZnChl-e6/TiO2) are 400, 660 and 800 nm, respectively. Especially the IPCE value at 800 nm (7.5%) is larger than that of 660 nm (6.9%). This result indicates that ZnChl-e6 molecules is aggregated or formed dimer on a nanocrystalline TiO2 layer onto OTE and the absorption band is shifted to near IR region. The photocurrent action spectrum of ZnChl-e6 and cholic acid adsorbed TiO2 layer onto OTE (ZnChl-e6-Cho/TiO2 is similar to that of the UV-vis absorption spectrum in methanol solution, and IPCE values at 400 and 660 nm (8.1%) increase and the IPCE value at 800 nm (4.1%) decreases, indicating that the aggregation of ZnChl-e6 molecules on the TiO2 is suppressed by cholic acid. By using ZnChl-e6-Cho/TiO2, the short-circuit photocurrent density and open-circuit photovoltage also increase compared with that of ZnChl-e6 adsorbed nanocrystalline TiO2 electrode.

Kunachowicz D., Kłosowska K., Sobczak N., Kepinska M.

The increasing incidence of breast cancers (BCs) in the world population and their complexity and high metastatic ability are serious concerns for healthcare systems. Despite the significant progress in medicine made in recent decades, the efficient treatment of invasive cancers still remains challenging. Chemotherapy, a fundamental systemic treatment method, is burdened with severe adverse effects, with efficacy limited by resistance development and risk of disease recurrence. Also, current diagnostic methods have certain drawbacks, attracting attention to the idea of developing novel, more sensitive detection and therapeutic modalities. It seems the solution for these issues can be provided by nanotechnology. Particularly, quantum dots (QDs) have been extensively evaluated as potential targeted drug delivery vehicles and, simultaneously, sensing and bioimaging probes. These fluorescent nanoparticles offer unlimited possibilities of surface modifications, allowing for the attachment of biomolecules, such as antibodies or proteins, and drug molecules, among others. In this work, we discuss the potential applicability of QDs in breast cancer diagnostics and treatment in light of the current knowledge. We begin with introducing the molecular and histopathological features of BCs, standard therapeutic regimens, and current diagnostic methods. Further, the features of QDs, along with their uptake, biodistribution patterns, and cytotoxicity, are described. Based on the reports published in recent years, we present the progress in research on possible QD use in improving BC diagnostics and treatment efficacy as chemotherapeutic delivery vehicles and photosensitizing agents, along with the stages of their development. We also address limitations and open questions regarding this topic.

Ihalagedara H.B., Xu Q., Greer A., Lyons A.M.

AbstractPhotochemical generation of singlet oxygen (1O2) often relies on homogenous systems; however, a dissolved photosensitizer (PS) may be unsuitable for some applications because it is difficult to recover, expensive to replenish, and hazardous to the environment. Isolation of the PS onto a solid support can overcome these limitations, but implementation faces other challenges, including agglomeration of the solid PS, physical quenching of 1O2 by the support, photooxidation of the PS, and hypoxic environments. Here, we explore a superhydrophobic polydimethylsiloxane (SH‐PDMS) support coated with the photosensitizer 5,10,15,20‐tetrakis(pentafluorophenyl)‐21H,23H‐porphyrin (TFPP). This approach seeks to address the challenges of a heterogeneous system by using a support that exhibits low 1O2 physical quenching rates, a fluorinated PS that is chemically resistant to photooxidation, and a superhydrophobic surface that entraps a layer of air, thus preventing hypoxia. Absorbance and fluorescence spectroscopy reveal the monomeric arrangement of TFPP on SH‐PDMS surfaces, a surprising but favorable characteristic for a solid‐phase PS on 1O2 yields. We also investigated the effect of incident wavelength on 1O2 yields for TFPP in aqueous solution and immobilized on SH‐PDMS and found overall yields to be dependent on the absorption coefficient, while the yield per absorbed photon exhibited wavelength independence, in accordance with Kasha‐Vavilov's rule.

Rempel Andrey A., Ovchinnikov Oleg V., Weinstein Ilya A., Rempel Svetlana V., Kuznetsova Yulia V., Naumov Andrei V., Smirnov Mikhail S., Eremchev Ivan Yu., Vokhmintsev Alexander S., Savchenko Sergey S.

Quantum dots are the most exciting representatives of nanomaterials. They are synthesized using advanced methods of nanotechnology pertaining to both inorganic and organic chemistry. Quantum dots possess unique physical and chemical properties; therefore, they are used in very different fields of physics, chemistry, biology, engineering and medicine. It is not surprising that the Nobel Prize in chemistry in 2023 was given for discovery and synthesis of quantum dots. This review addresses modern methods for the synthesis of quantum dots and their optical properties and practical applications. In the beginning, a short insight into the history of quantum dots is given. Many gifted scientists, including chemists and physicists, were engaged in these studies. The synthesis of quantum dots in solid and liquid matrices is described in detail. Quantum dots are well-known owing to their unique optical properties; that is why the attention in the review is focused on the quantum-size effect. The causes for fascinating blinking of quantum dots and techniques for observation of a single quantum dot are considered. The last part of the review describes mportant applications of quantum dots in biology, medicine and quantum technologies.The bibliography includes 772 references.

Białowąs W., Boudjemaa R., Steenkeste K., Nyssen P., Hoebeke M., Lulek J., Fontaine-Aupart M.P., Schneider R.

The photoproduction of reactive oxygen species (ROS) by semiconductor nanocrystals is of high interest for biological and environmental applications. Herein, water-dispersible 3-mercaptopropionic (MPA)-capped (CuInS2)x(ZnS)1-x quantum dots (ZCIS@MPA QDs) were prepared from dodecanethiol-capped ZCIS QDs by a ligand exchange and their photoreactivity was evaluated. By combining colorimetric and fluorescent probes with electron spin resonance (ESR) measurements, we showed that ZCIS@MPA QDs can photogenerate ROS like hydroxyl ●OH and superoxide O2●- radicals and singlet oxygen 1O2 that alter the MPA ligand and participate in photoluminescence quenching. The phototoxicity of ZCIS@MPA QDs against S. aureus bacteria and the inhibition of the cell growth on a surface were further investigated. These deleterious effects of ROS photoproduced by ZCIS@MPA QDs could significantly be reduced by coupling the antioxidant glutathione peptide with the QDs. Our findings enrich the understanding of photochemical reactions mediated by ZCIS@MPA QDs but also provide new pathways for ROS production, even under ambient light, that may be valuable for antibacterial applications like surface disinfection.

Luo S., Zhang Y., Zhu Y., Wang X., Ran X., He Y., Kuang Y., Chi Z., Guo L.

Karabuga M., Erdogan S., Filikci K., Hazıroglu R., Tuncel M., Cengiz M.

Radiotherapy is one of the cancer treatment options in which ionizing radiation is used. While the ionizing radiation used here damages the tumor cells, it also damages the surrounding healthy cells and tissues. One of the approaches used to reduce the undesirable side effects and increase the therapeutic efficacy of radiotherapy is the use of radiosensitizers. Up to now, different radiosensitizers have been investigated for this purpose and recently, nanotechnology-based radiosensitizer research has attracted much attention. In this study, the therapeutic efficacy of tumor-targeted, nano-sized liposomal radiosensitizers containing quantum dots-photosensitizer conjugate was evaluated in vivo. It was aimed to destroy more tumor cells by using same the radiation doses routinely used in cancer treatment in radiation oncology clinics or to destroy about the same amount of tumor cells by using lower radiation doses than the routinely used clinical dose. For this purpose, nano-sized, PEG-coated, and folic acid-modified tumor-specific liposomes loaded with quantum dots (QD = CdSe/ZnS) - photosensitizer (Ce6 = Clorine-e6) conjugate was prepared and their therapeutic efficacy was evaluated in 4T1 murine breast cancer cell tumor-bearing mice. Following the single dose of 10Gy 6 MV X-ray irradiation after administration of liposomal radiosensitizer, changes in animals' weights and tumor volumes were measured and animal survival was monitored to evaluate the efficacy of the treatment. Histopathological studies were also performed to examine possible damage to the tumor and normal tissues. In control groups, only X-ray irradiation was applied or no treatment was applied to mice. The results showed that the liposomal radiosensitizer plus radiotherapy killed more cancer cells than radiotherapy alone. While tumor volumes increased in the control group, approximately a 39% reduction in tumor volumes was observed in mice treated with x-ray irradiation following administration of the liposomal radiosensitizer. The obtained results showed that nano-sized liposomal radiosensitizers could be a promising radiosensitizer to achieve better treatment efficacy in radiotherapy by applying fewer radiation doses compared to clinically used radiation doses.

Khan Z.U., Khan L.U., Uchiyama M.K., Prado F.M., Faria R.L., Costa I.F., Miyamoto S., Araki K., Gidlund M., Brito H.F., Di Mascio P.

It is highly desirable in biomedical sciences to utilize the multifunctional nanoparticles of similar size with tunable emission. Since the optoelectronic properties of quantum dots (QDs) originate from size-dependent quantum confinement effects, we developed an alternate approach to synthesize color-tunable CdSe/ZnS QDs based on interfacial ion exchange (predominantly exchange of Se2– by S2– anions), using 1-dodecanethiol and oleylamine solvent systems as a sensitive parameter. The wide-range color-tunability (490–570 nm) was achieved unexpectedly as a result of interfacial alloying without inducing a significant change in the size (from 4.45 to 4.81 nm) of QDs. The local atomic structure order, chemical composition, and nature of alloying in QDs were unraveled by XAFS data analysis. Owing to the molecular-like sensitization behavior, the QDs were evaluated for singlet molecular oxygen (1O2) efficiency. They were further studied in RAW 264.7 macrophages for biocompatibility, bioimaging, and delivering pathways for use in future photodynamic therapy (PDT). The QDs demonstrated efficient singlet molecular oxygen (1O2) quantum yields (ΦQDs) of 14, 12, and 18% for QDs (I), QDs (II), and QDs (III), respectively. The QD-treated cells presented high cell viability above 85% and induced no cell activation. Fluorescence and transmission electron microscopy (TEM) images of cells manifested a considerable amount of QDs in the vicinity of the cell membrane and intracellular regions. The pathway-specific inhibition measurements revealed that the QDs were internalized by cells via energy-dependent endocytosis, predominantly macropinocytosis and other receptor-mediated endocytic pathways, and accumulated them presumably in endosome/lysosomes. This study will open new possibilities for engineering interfacial alloying-based tunable emission QDs and pathway-specific delivery of QD-based theranostics into a site of interest for simultaneous bioimaging and PDT.

Öztürk D., Ömeroğlu İ., Durmuş M.

Quantum dots (QDs) are a new class of nanomaterials and their photophysical and photochemical properties are promising for future biological applications such as cancer diagnosis and treatment by photodynamic therapy (PDT). This chapter summarizes the progress research of QDs about their synthesis methods, photophysical and photochemical studies, in vitro and in vivo applications in PDT. Significantly, red to near-infrared (R/NIR) QDs are also preferred for both in vitro and in vivo bioimaging, cancer therapy including chemotherapy, photothermal therapy, PDT, and synergistic therapy. However, QDs are facing some challenges in practical applications. Synthesis of QDs should be green, low cost, and reproducible. NIR region emissive QDs with high quantum yield in aqueous solution are desired in vivo applications and phototherapy. It is important to develop these promising materials that will be used in many biological applications in the future. In vitro and in vivo applications for cancer treatment are limited in the literature. For this reason, it is expected that QDs will be used in the diagnosis and treatment of diseases on human health.

Karabuga M., Erdogan S., Timur S.S., Vural I., Çalamak S., Ulubayram K.

Dapkute D., Pleckaitis M., Bulotiene D., Daunoravicius D., Rotomskis R., Karabanovas V.

Nanotechnology has emerged as a promising solution to permanent elimination of cancer. However, nanoparticles themselves lack specificity to tumors. Due to enhanced migration to tumors, mesenchymal stem cells (MSCs) were suggested as cell-mediated delivery vehicles of nanoparticles. In this study, we have constructed a complex composed of photoluminescent quantum dots (QDs) and a photosensitizer chlorin e6 (Ce6) to obtain multifunctional nanoparticles, combining cancer diagnostic and therapeutic properties. QDs serve as energy donors-excited QDs transfer energy to the attached Ce6 via Förster resonance energy transfer, which in turn generates reactive oxygen species. Here, the physicochemical properties of the QD-Ce6 complex and singlet oxygen generation were measured, and the stability in protein-rich media was evaluated, showing that the complex remains the most stable in protein-free medium. In vitro studies on MSC and cancer cell response to the QD-Ce6 complex revealed the complex-loaded MSCs' potential to transport theranostic nanoparticles and induce cancer cell death. In vivo studies proved the therapeutic efficacy, as the survival of tumor-bearing mice was statistically significantly increased, while tumor progression and metastases were slowed down.

Huang L., Asghar S., Zhu T., Ye P., Hu Z., Chen Z., Xiao Y.

Lins P.M., Ribovski L., Sampaio I., Santos O.A., Zucolotto V., Cancino-Bernardi J.

Nanomedicine is a research area at the interface between nanotechnology and biotechnology that aims at developing nanosystems for diagnosis and therapy. As active materials to be used in both diagnosis and therapy, inorganic nanoparticles (INPs), in particular, are of great interest in nanomedicine. INPs have been applied in several therapy strategies, including active drug delivery, hyperthermia, and magnetothermia against cancer, and their use offer advantages in medical applications due to their physicochemical characteristics, such as localized surface plasmon resonance (LSPR) effect—present in Au and Ag nanoparticles, for example—and the magnetic and photoluminescence properties of magnetic nanoparticles and quantum dots, respectively. The application of INPs in molecular imaging and drug delivery has benefited from their reduced size, which allows the INPs to overcome cell barriers that conventional drugs cannot do, such as the blood–brain barrier. In addition to the physical and chemical properties of the INPs, their surface modifications using biomolecules provide specificity to the nanocarrier systems to increase absorption and biodistribution. This chapter describes the main characteristics and the most relevant applications of gold, silver, quantum dots, ceramics, and magnetic nanoparticles in biomedicine.

Sewid F.A., Skurlov I.D., Kurshanov D.A., Orlova A.O.

• QDs-TPP hybrid structures have higher SO generation compared to free TPP. • MCD spectra confirm TPP remain monomers on QDs surface in hybrid structures. • FRET fully used to generate SO as there are no new nonradiative channels in structures. Photophysical properties of hybrid structures based on CdSe/ZnS quantum dots (QDs) and tetraphenylporphyrin (TPP) molecules have been studied. The hybrid structures are characterized by higher singlet oxygen (SO) generation compared to free TPP molecules due to high intracomplex Förster Resonance Energy Transfer (FRET) efficiency and saving TPP in the monomeric form in the hybrid structures. We show that all energy transferred from QDs to TPP is fully used to generate singlet oxygen since there are no new nonradiative channels in the structures. We believe that our result will stimulate renewed interest in QD based structures with photosensitizers as theranostics agents.

Kirsanova D.Y., Gadzhimagomedova Z.M., Maksimov A.Y., Soldatov A.V.

: According to statistics, cancer is the second leading cause of death in the world. Thus, it is important to solve this medical and social problem by developing new effective methods for cancer treatment. An alternative to more well-known approaches, such as radiotherapy and chemotherapy, is photodynamic therapy (PDT), which is limited to the shallow tissue penetration (< 1 cm) of visible light. Since the PDT process can be initiated in deep tissues by X-ray irradiation (X-ray induced PDT, or XPDT), it has a great potential to treat tumors in internal organs. The article discusses the principles of therapies. The main focus is on various nanoparticles used with or without photosensitizers, which allow the conversion of X-ray irradiation into UV-visible light. Much attention is given to the synthesis of nanoparticles and analysis of their characteristics, such as size and spectral features. The results of in vitro and in vivo experiments are also discussed.

Ravaro L.P., Ford P.C., de Camargo A.S.

A novel nanocomposite luminescent material was prepared by taking advantage of the versatile wet impregnation method for the dispersion of CdTe quantum dots (QDs) into mesoporous silica host matrix and thus providing great interaction between oxygen and QDs, with potential application in an optical oxygen sensor. The optical/spectroscopic properties of the QDs suspended in aqueous media and incorporated in mesoporous silica were evaluated as a function of aging time, temperature variation and oxygen concentration. Luminescence quenching studies were carried out for both QDs suspended in solution and loaded into the silica matrix, in the presence of varying O2 concentration. By Stern-Volmer plot analysis, obtained at different temperatures, it was possible to verify the existence of two types of emission quenching mechanisms for CdTe QDs. After aging for 120 days at room temperature, the QDs in colloidal suspension displayed a small red-shifted emission, which was interpreted as a decreased bandgap energy owing to the increase in the nanocrystal size. In contrast, the emission spectrum of CdTe QDs loaded into the mesoporous SiO2 matrix remained unchanged after aging for the same time at ambient temperature. The presented results will contribute to the discernment of oxygen quenching mechanisms and chemical stability of optical sensors based on CdTe QDs.