Biological Optical Window Research Articles

Hydrogenation of di(methoxo)tetraphenylporphyrin phosphorus(V) to isobacteriochlorin, chlorin, and phlorin complex with long-wavelength absorption band

We report the synthesis of nonmetal high-valent phosphorus(V) hydroporphyrin complexes: PV-isobacteriochlorin, PV-chlorin, and two isomers of PV-phlorin, via simple hydrogenation of di(methoxo)tetraphenylporphyrin phosphorus(V) with a hydrogen source and Pd/C catalyst. These PV-hydroporphyrin complexes exhibit long-wavelength absorption bands in the biological optical window. PV-isobacteriochlorin and PV-chlorin complexes are stable against auto-oxidation and exhibit the photoproduction of singlet oxygen under red light irradiation.

Heat generation on Fe3O4@SiO2@Au core-shell structures using the synergy of an alternating magnetic field and NIR laser light within Ist biological optical window

Fe3O4@SiO2@Au heterostructures were prepared using a three-step process that included (I) non-hydrolytic thermal decomposition synthesis of magnetic nanoparticles with cubic morphology, (II) deposition of the amorphous silica shell using wet-chemistry technique and (III) reduction of the chemisorbed gold cations using NaBH4 agent. The energy conversion was performed using the action of the alternating magnetic field (AMF) and NIR laser light (808 nm) under separate and mutual contactless stimulation. It was found that the Fe3O4@SiO2@Au heterostructures are highly responsive to both stimuli with the predominance of the NIR heat-induced mechanism. The dual action of AMF and NIR for optimized parameters is advantageous since heating occurs faster and more efficiently (SAR 1300 W/g). The final desirable temperature can be tuned by the adjustment of the AMF, NIR parameters, and particle concentration. The heterostructures show a cytostatic effect in contact with the breast cancer lines SK-BR-3, MCF-7, and MDA-MB-231.

Core-multishell lanthanide-doped nanocomposite by one-pot synthesis for NIR-II emissions-based temperature sensing

The performances of nanothermometers based on visible light are inevitably degraded in biological applications because visible light is greatly weakened after passing through tissues. Herein, in view of the second biological optical transparency window, a type of tailored core-multishell lanthanide-doped nanocomposite was synthesized with facile one-pot coprecipitation method to supplant complex method demanding stepwise thermal decomposition. Proved to have excellent dispersibility, crystallinity, stability and luminous efficiency, the nanocomposite is capable of enhanced NIR-II emissions and a broad temperature detection scope based on three kinds of spectral parameters relevant to its unique core-multishell structure. The maximum absolute and relative sensitivity of luminescence intensity ratios in low temperature range can reach up to 11.3% K−1 and 1.27% K−1, respectively, and a theoretical derivation is provided to address the peculiar V-shaped trend of NIR-II luminescence lifetime. The prepared nanocomposite can serve as a promising candidate for optical thermometer in the fields of cryoablation of diseased tissues and industrial applications in strong magnetic or radiofrequency fields.

A Dinuclear Osmium(II) Complex Near-Infrared Nanoscopy Probe for Nuclear DNA.

With the aim of developing photostable near-infrared cell imaging probes, a convenient route to the synthesis of heteroleptic OsII complexes containing the Os(TAP)2 fragment is reported. This method was used to synthesize the dinuclear OsII complex, [{Os(TAP)2}2tpphz]4+ (where tpphz = tetrapyrido[3,2-a:2',3'-c:3″,2''-h:2‴,3'''-j]phenazine and TAP = 1,4,5,8- tetraazaphenanthrene). Using a combination of resonance Raman and time-resolved absorption spectroscopy, as well as computational studies, the excited state dynamics of the new complex were dissected. These studies revealed that, although the complex has several close lying excited states, its near-infrared, NIR, emission (λmax = 780 nm) is due to a low-lying Os → TAP based 3MCLT state. Cell-based studies revealed that unlike its RuII analogue, the new complex is neither cytotoxic nor photocytotoxic. However, as it is highly photostable as well as live-cell permeant and displays NIR luminescence within the biological optical window, its properties make it an ideal probe for optical microscopy, demonstrated by its use as a super-resolution NIR STED probe for nuclear DNA.

Time-Resolved and Temperature-Dependent Fractional Amplitude Contributions to the Broadband Emission of CdSe Quantum Dots

The broadband spontaneous emission of excitons in CdSe quantum dots (QDs) is of great interest for the spectral imaging of living organisms or specific substances in the visible spectral region as well as in the biological optical window near the infrared spectral region. Semiconductor QDs that are near the bulk Bohr radius exhibit wide spectral tunability and high color purity due to quantum confinement of excitons within the dot boundary. However, with reducing dot size, the role of the surface-trapped state increases. The temperature-dependent photoluminescence (PL) confirms this with a ~3:1 emission intensity decrease from the surface-trapped state compared to the band edge. Large crystal irregularity, dangling ions, and foreign molecules can introduce new electronic transitions from surface-trapped states that provide broad spontaneous emission in the spectral region from visible to near IR in addition to the band edge emission. The time-resolved PL analyzed the fractional contributions of band edge, surface-trapped states, and possible intermediate trapped states to the broad spectral emission in order to characterize the CdSe QDs.

A rational design of multimodal asymmetric nanoshells as efficient tunable absorbers within the biological optical window

In this work, the optical properties of asymmetric nanoshells with different geometries are comprehensively investigated in the quasi-static regime by applying the dipolar model and effective medium theory. The plasmonic behaviors of these nanostructures are explained by the plasmon hybridization model. Asymmetric hybrid nanoshells, composed of off-center core or nanorod core surrounded by a spherical metallic shell layer possess highly geometrically tunable optical resonances in the near-infrared regime. The plasmon modes of this nanostructures arise from the hybridization of the cavity and solid plasmon modes at the inner and outer surfaces of the shell. The results reveal that the symmetry breaking drastically affects the strength of hybridization between plasmon modes, which ultimately affects the absorption spectrum by altering the number of resonance modes, their wavelengths and absorption efficiencies. Therefore, offsetting the spherical core as well as changing the internal geometry of the nanoparticle to nanorod not only shift the resonance frequencies but can also strongly modify the relative magnitudes of the absorption efficiencies. Furthermore, higher order multipolar plasmon modes can appear in the spectrum of asymmetric nanoshell, especially in nanoegg configuration. The results also indicate that the strength of hybridization strongly depends on the metal of shell, material of core and the filling factor. Using Au-Ag alloy as a material of the shell can provide red-shifted narrow resonance peak in the near-infrared regime by combining the specific features of gold and silver. Moreover, inserting a high permittivity core in a nanoshell corresponds to a red-shift, while a core with small dielectric constant results in a blue-shift of spectrum. We envision that this research offers a novel perspective and provides a practical guideline in the fabrication of efficient tunable absorbers in the nanoscale regime.

Three-Photon Spectroscopy of Porphyrins.

Recent advances in laser technology have made three-photon (3P) microscopy a real possibility, raising interest in the phenomenon of 3P absorption (3PA). Understanding 3PA of organic chromophores is especially important in view of those imaging applications that rely on exogenous probes, whose optical properties can be manipulated and optimized. Here, we present measurements and theoretical analysis of the degenerate 3PA spectra of several phosphorescent metalloporphyrins, which are used in the construction of biological oxygen probes. The effective 3PA cross sections (σ(3)) of these porphyrins near 1700 nm, a new promising biological optical window, were found to be on the order of 1000 GM3 (1 GM3 = 10-83 cm6 s2), therefore being among the highest values reported to date for organic chromophores. To interpret our data, we developed a qualitative four-state model specific for porphyrins and used it in conjunction with quantitative analysis based on the time-dependent density functional theory (TDDFT)/a posteriori Tamm-Dancoff approximation (ATDA)/sum-over-states (SOS) formalism. The analysis revealed that B (Soret) state plays a key role in the enhancement of 3PA of porphyrins in the Q band region, while the low-lying two-photon (2P)-allowed gerade states interfere negatively and diminish the 3PA strength. This study features the first systematic examination of 3PA properties of porphyrins, suggesting ways to improve their performance and optimize them for imaging and other biomedical applications.

Morphological and Surface-State Challenges in Ge Nanoparticle Applications.

The intrinsic properties of Ge in tandem with advances in its nanostructuring have resulted in its increased attention in a variety of fields as an alternative to traditional group 12-14 and 14-16 nanoparticles (NPs). The small band gap and size-dependent development of the optical properties in tandem with their good charge transport properties make Ge NPs a suitable material for optoelectronic devices. The low toxicity of Ge, together with its IR photoluminescence (PL) that overlaps with desirable biological optical windows used for tissue imaging, allows the exploitation of these materials in the field of bioimaging and as drug carriers. In addition, the ability of germanium to both exhibit high mechanical stability in its NP form and alloy with lithium and sodium metals has led to it being a highly attractive material for next-generation lithium ion and beyond-lithium batteries. While it is attracting considerable attention in a variety of areas, research on Ge NPs is still relatively nascent. Fundamental aspects of this material, such as its Bohr radius and the origin of different observed PLs, are still under debate. Moreover, the ability to produce Ge NPs with controlled dimensions and morphology is not yet as mature as for other classes of nanomaterials. In this review, the mechanisms and origins of these properties will be introduced, which we then relate to specific applications presented in the literature.

Cr4+ activated NIR-NIR multi-mode luminescent nanothermometer for double biological windows

Remote temperature sensing in biological media is used to monitor intracellular evolutionary process reliably, and is potentially applied in the field of diagnostics and therapeutics. Ideally, such nanothermometers should be functional in biological optical transparency windows across a wide range of broad absorption and emission bands, strong luminescence and larger Stokes shift. Here, this is achieved via using NIR-to-NIR transition metal (Cr4+)-doped aluminosilicate nanoparticles as multiparametric thermal sensing probes. They can be excited in first biological window and emitted in second biological window, allowing for large optical penetration into tissues while maintaining high-spatial resolution. We also demonstrate that the phenomena of temperature-induced population redistribution and temperature-induced spectral red-shift (maximum thermal sensitivity is 0.61% °C−1, superior to the most of the current materials), essentially allow for a multi-mode thermal sensing within a single probe towards to a very different optical response. We believe that these findings can be expanded a wide range of promising applications using transition metal-activated luminescent nanoparticles as nanothermometers in deep tissue temperature measurements of biological and biochemical.

Plasmonic Nanoassemblies: Tentacles Beat Satellites for Boosting Broadband NIR Plasmon Coupling Providing a Novel Candidate for SERS and Photothermal Therapy.

Optical theranostic applications demand near-infrared (NIR) localized surface plasmon resonance (LSPR) and maximized electric field at nanosurfaces and nanojunctions, aiding diagnosis via Raman or optoacoustic imaging, and photothermal-based therapies. To this end, multiple permutations and combinations of plasmonic nanostructures and molecular "glues" or linkers are employed to obtain nanoassemblies, such as nanobranches and core-satellite morphologies. An advanced nanoassembly morphology comprising multiple linear tentacles anchored onto a spherical core is reported here. Importantly, this core-multi-tentacle-nanoassembly (CMT) benefits from numerous plasmonic interactions between multiple 5 nm gold nanoparticles (NPs) forming each tentacle as well as tentacle to core (15 nm) coupling. This results in an intense LSPR across the "biological optical window" of 650-1100 nm. It is shown that the combined interactions are responsible for the broadband LSPR and the intense electric field, otherwise not achievable with core-satellite morphologies. Further the sub 80 nm CMTs boosted NIR-surface-enhanced Raman scattering (SERS), with detection of SERS labels at 47 × 10-9 m, as well as lower toxicity to noncancerous cell lines (human fibroblast Wi38) than observed for cancerous cell lines (human breast cancer MCF7), presents itself as an attractive candidate for use as biomedical theranostics agents.

LiAl5O8:Fe3+ and LiAl5O8:Fe3+, Nd3+ as a New Luminescent Nanothermometer Operating in 1st Biological Optical Window.

New types of contactless luminescence nanothermometers, namely, LiAl5O8:Fe3+ and LiAl5O8:Fe3+, Nd3+ are presented for the first time, revealing the potential for applications in biological systems. The temperature-sensing capability of the nanocrystals was analyzed in wide range of temperature (−150 to 300 °C). The emission intensity of the Fe3+ ions is affected by the change in temperature, which induces quenching of the 4T1 (4G) → 6A1 (6S) Fe3+ transition situated in the 1st biological window. The highest relative sensitivity in the temperature range (0 to 50 °C) was found to be 0.82% °C (at 26 °C) for LiAl5O8: 0.05% Fe3+ nanoparticles that are characterized by long luminescent lifetime of 5.64 ms. In the range of low and high temperatures the Smax was calculated for LiAl5O8:0.5% Fe3+ to be 0.92% °C at −100 °C and for LiAl5O8:0.01% Fe3+ to be 0.79% °C at 150 °C. The cytotoxicity assessment carried out on the LiAl5O8:Fe3+ nanocrystals, demonstrated that they are biocompatible and may be utilized for in vivo temperature sensing. The ratiometric luminescent nanothermometer, LiAl5O8:Fe3+, Nd3+, which was used as a reference, possesses an Smax = 0.56%/°C at −80 °C, upon separate excitation of Fe3+ and Nd3+ ions using 266 nm and 808 nm light, respectively.

Synthesis of molybdenum oxide nanoparticles by nanosecond laser ablation

Phothermal therapy (PTT) is one of the most promising techniques to treat cancer. Finding the ideal PTT agent nanomaterial has remained a challenge and has brought the interest of several researchers. In this work, we report the synthesis of molybdenum oxide (MoOx) nanoparticles (NPs), which exhibit absorption in the biological optical window ~840 nm, by using the laser ablation of solids in liquids (LASL) technique with nanosecond (ns) pulses. A Nd:YAG laser was used to synthesize the NPs in deionized (DI) water, free of surfactants or additives, which were optically characterized by absorption spectroscopy and TEM-EDX microscopy. Semi spherical NPs with a suitable average size and shape for potential use as PTT agents were obtained by laser ablation and ablation + fragmentation. The calculated band gap is 3.1 eV, which corresponds to MoO3. Micro-Raman spectroscopy studies determined that these NPs are composed of amorphous molybdenum oxide hydrates (MoO3 · xH2O).

Defective [Bi2 O2 ]2+ Layers Exhibiting Ultrabroad Near-Infrared Luminescence.

Aurivillius phases have been routinely known as excellent ferroelectrics and have rarely been deemed as materials that luminesce in the near-infrared (NIR) region. Herein, it is shown that the Aurivillius phases can demonstrate broadband NIR luminescence that covers telecommunication and biological optical windows. Experimental characterization of the model system Bi2.14 Sr0.75 Ta2 O9-x , combined with theoretical calculations, help to establish that the NIR luminescence originates from defective [Bi2 O2 ]2+ layers. Importantly, the generality of this finding is validated based on observations of a rich bank of NIR luminescence characteristics in other Aurivillius phases. This work highlights that incorporating defects into infinitely repeating [Bi2 O2 ]2+ layers can be used as a powerful tool to space-selectively impart unusual luminescence emitters to Aurivillius-phase ferroelectrics, which not only offers an optical probe for the examination of defect states in ferroelectrics, but also provides possibilities for coupling of the ferroelectric property with NIR luminescence.

Praseodymium doped YF3:Pr3+ nanoparticles as optical thermometer based on luminescence intensity ratio (LIR) – Studies in visible and NIR range

Luminescent YF3 nanoparticles doped with Pr3+ activator ion have been successfully synthesized via a facile hydrothermal approach for their application as a multi-range optical sensor of temperature. The product synthesized shows intense yellow luminescence at 457 nm laser excitation, and the emission spectra were recorded from 475 to 1650 nm, showing the presence of sharp emission peaks in the measured spectral range. The intensity of the observed emission bands typical of Pr3+ ion changes with temperature significantly. Hence, the intensity ratios of the thermalized emission bands were determined in the temperature range from 293 to 421 K, and they were calibrated for thermal sensing purposes. High relative sensitivity values, ranging from 0.6 to 1.2 %K−1, were found for the emission bands of the thermally-coupled 3P1 and 3P0 excited states located around 522–537, 586–603 and 700–723 nm. The temperature calibration based on the thermalized 3P1→3F4 and 3P0→3F4 bands located in the first biological optical window (650–950 nm), may be especially useful for potential biological applications.

Nd3+ doped Gd3Sc2Al3O12 nanoparticles: towards efficient nanoprobes for temperature sensing.

Development of contactless temperature-probing nanoplatforms based on thermosensitive near-infrared (NIR) light-emitting nanoparticles opens up new horizons for biomedical theranostics at a deep tissue level. Here, we report on the crystallinity and relative thermal sensitivity of NIR emitting Nd3+ doped Gd3Sc2Al3O12 (GSAG:Nd3+) nanoparticles synthesized by a solvothermal method. The obtained nanoparticles are well-crystallized, with sizes less than 100 nm, and can be dispersed in water without any additional functionalization. Upon excitation at 806 nm, the nanoparticles exhibit emission in the first and second biological optical transparency windows. The temperature sensing properties were evaluated from the luminescence intensity ratio of the thermally coupled emission lines corresponding to the R1, R2→Z5 transitions between the Stark sublevels of the 4F3/2 and 4I9/2 electronic states of Nd3+ in the physiological temperature range of 20-50 °C. GSAG:Nd3+ nanoparticles exhibit a maximal relative thermal sensitivity of 0.20% °C-1, higher than that of YAG:Nd3+ nanoparticles used as a control, due to the difference in the crystal field of the host matrices. A higher synthesis temperature in the range of 300-400 °C was also provided to improve the crystallinity of the GSAG:Nd3+ nanoparticles which results in a higher relative thermal sensitivity. Our results demonstrate the potential of GSAG:Nd3+ nanoparticles as luminescence nanothermometers and emphasize the interest of the GSAG matrix itself, which with the presence of Gd, could lead to multimodal diagnostic applications in nanothermometry and magnetic resonance imaging (MRI).

Red-Tuning of the Channelrhodopsin Spectrum Using Long Conjugated Retinal Analogues.

As optogenetic studies become more popular, the demand for red-shifted channelrhodopsin is increasing, because blue-green light is highly scattered or absorbed by animal tissues. In this study, we developed a red-shifted channelrhodopsin by elongating the conjugated double-bond system of the native chromophore, all -trans-retinal (ATR1). Analogues of ATR1 and ATR2 (3,4-didehydro-retinal) in which an extra C═C bond is inserted at different positions (C6-C7, C10-C11, and C14-C15) were synthesized and introduced into a widely used channelrhodopsin variant, C1C2 (a chimeric protein of channelrhodopsin-1 and channelrhodopsin-2 from Chlamydomonas reinhardtii). C1C2 bearing these retinal analogues as chromophores showed broadened absorption spectra toward the long-wavelength side and photocycle intermediates similar to the conducting state of channelrhodopsin. However, the position of methyl groups on the retinal polyene chain influenced the yield of the pigment, absorption maximum, and photocycle pattern to a variable degree. The lack of a methyl group at position C9 of the analogues considerably decreased the yield of the pigment, whereas a methyl group at position C15 exhibited a large red-shift in the absorption spectra of the C1C2 analogue. Expansion of the chromophore binding pocket by mutation of aromatic residue Phe265 to Ala improved the yield of the pigment bearing elongated ATR1 analogues without a great alteration of the photocycle kinetics of C1C2. Our results show that elongation of the conjugated double-bond system of retinal is a promising strategy for improving the ability of channelrhodopsin to absorb long-wavelength light passing through the biological optical window.

Upconverting lanthanide doped fluoride NaLuF4:Yb3+-Er3+-Ho3+ - optical sensor for multi-range fluorescence intensity ratio (FIR) thermometry in visible and NIR regions

Luminescent materials co-doped with Er3+-Ho3+ activator ions can work as multi-range Vis-NIR optical sensors of temperature. The upconverting NaLuF4:16%Yb3+-2%Er3+-0.5%Ho3+ hexagonal microcrystals, were successfully synthesized under hydrothermal conditions. The material obtained showed bright yellow up-conversion luminescence, under 975 nm CW laser irradiation. The emission spectra were measured in a broad spectral range, i.e. 450–1650 nm, revealing the presence of intense emission bands both in the visible and NIR range. The intensities of the Vis-NIR emission bands characteristic of Er3+ and Ho3+ changed with temperature, and the evolution of their intensity ratios were correlated with temperature and calibrated. The high sensitivity found for the intensity ratio coming from the Ho3+: 5I5→5I8 (887 nm) and Er3+: 4I9/2→4I15/2 (817 nm) transitions, located in the first biological optical window, is useful for optical thermometry applications.

Superbroad near-infrared photoluminescence from bismuth-doped CsPbI_3 perovskite nanocrystals

Bismuth-doped materials show fascinating near-infrared (NIR) photoluminescence (PL) properties. However, synthesizing Bi-doped, NIR-luminescent, nanometer-sized materials with high PL quantum yields remains challenging. Here, Bi-doped CsPbI3 perovskite nanocrystals (NCs) with an average size less than 10 nm and showing a superbroad NIR PL covering the telecommunication and second biological optical windows were achieved. The NIR PL quantum yield of these NCs is up to 7.17% with the Bi doping concentration of 0.074%. Additionally, efficient energy transfer from the semiconducting CsPbI3 to bismuth-related active center can be realized. We anticipate that the developed systems may find applications in optoelectronic and photonic devices as well as biological imaging. This work enriches the bank of Bi-doped luminescent materials, and might stimulate research interest for synthesizing other classes of Bi-activated nanomaterials.

Critical Overview of the Use of Ru(II) Polypyridyl Complexes as Photosensitizers in One-Photon and Two-Photon Photodynamic Therapy.

Photodynamic Therapy (PDT) is an emerging technique to treat certain types of cancer, bacterial, fungal, and viral infections, and skin diseases. In past years, different research groups developed new ruthenium-containing photosensitizers (PSs) with tuned photophysical and biological properties to better fit the requirements of PDT. In this Account, we report and discuss the latest results in this research area, emphasizing particularly our own research. For example, inspired by the DNA intercalating complex [Ru(bpy)2(dppz)]2+ (bpy = 2,2'-bipyridine; dppz = (dipyrido[3,2-a:2',3'-c]phenazine), a series of ruthenium complexes bearing differently functionalized dppz ligands were synthesized to target DNA. The introduction of the substituents on the dppz ligand did not reduce much the affinity of the complexes to DNA but highly affected their cellular uptake. The most effective complex in this series, [Ru(bpy)2(dppz-7-OMe)]2+, showed IC50 values in the low micromolar range against several types of cancer cells upon light irradiation and, importantly, a high phototoxic index (PI) of >150. This value is comparable to or even better than several PSs used in clinics under comparable experimental conditions. This compound was found to localize in the nucleus and to induce DNA damage in HeLa cells upon light irradiation. Interestingly, cells in the mitotic phase were found to be more affected and to have a different mechanism of cell death (apoptosis) upon light irradiation than those in the interphase (paraptosis). To take advantage of that, the PS was combined with a cell cycle inhibitor to synchronize cells in the mitotic phase, further improving the phototoxicity by a factor of 3.6. In addition, our group recently demonstrated that [Ru(bphen)2(benzene-1,2-dislufinate)] (bphen = 4,7-diphenyl-1,10-phenanthroline) localizes in mitochondria and has an IC50 value of 0.62 μM with a PI of over 80 in HeLa cells upon light irradiation at 420 nm. Interestingly, this complex was also found to efficiently kill Gram-positive Staphylococcus aureus under light irradiation. Antimicrobial PDT (aPDT) is another field of research where Ru(II) polypyridyl complexes can play an interesting role to fight antibiotics resistance. [Ru(dqpCO2Me)(ptpy)]2+ (dqpCO2Me = 4-methylcarboxy-2,6-di(quinolin-8-yl)pyridine), ptpy = 4'-phenyl-2,2':6',2″-terpyridine) is additionally efficient against Gram-negative Escherichia coli. The efficacy of positively charged Ru(II) PSs is related to their affinity to the negatively charged membrane of Gram-negative bacteria. A drawback of many Ru(II) polypyridyl PSs is their low absorption in the biological optical window (600-900 nm) where light penetration depth into tissue is the highest. The lowest energy transition in the UV/Vis spectra of Ru(II) polypyridyl complexes is usually a metal-to-ligand charge-transfer band. To shift the absorption into this range, tuning of the ligand system, for example, by extending π-systems, has been described in the literature. Another approach to make excitation in the optical biological window possible is Two-Photon Absorption (2PA). High photon density is needed and usually confocal laser beams are used for excitation. In collaboration with the Chao group, a series of homoleptic Ru(II) complexes bearing tertiary alkyl ammonium substituted bipyridine ligands with two photon cross sections between 185 and 250 GM at around 800 nm was tested in vitro. They showed IC50 values in the micromolar range and PIs between 103 and 313. The highly positive-charged complexes were found to enter the cell via endocytosis and to target lysosomes. Studies on 3D tumor cell spheroids, a model closer to real tumors than commonly used 2D cell monolayers, were also performed. It could be demonstrated that 2P-PDT treatment with 800 nm laser irradiation was significantly more effective than that with 450 nm laser irradiation.

Photostable upconverting and downconverting pH sensors based on combination of a colorimetric NIR indicator and stable inorganic phosphors as secondary emitters

New robust optical pH sensors rely on a combination of a photochemically stable NIR colorimetric aza-BODIPY dye and inorganic phosphors. Inner-filter effect is utilized to convert the colorimetric changes into a luminescence response. Chromium(III)-activated gadolinium aluminium borate and Egyptian Blue were used as inert reference phosphors, enabling two-wavelength ratiometric read-out in the emission and excitation mode, respectively. Additionally, we synthetized dually-emitting upconverting particles (UCPs) based on lanthanide-doped molybdates (NaCaY1−xLax(MoO4)3, La=Yb(III), Ho(III) and Tm(III)) featuring anti-Stokes emission peaks in the red/NIR spectral region (645/800nm). Upon NIR excitation (980nm) the NIR emission of the upconverting particles is modulated by the pH indicator, whereas the red emission serves as a reference. Importantly, the spectral properties of the pH sensor based on UCPs are fully compatible with the biological optical window.