Upon Ultraviolet Research Articles

Rapid, ultraviolet-induced, reversibly switchable wettability of superhydrophobic/superhydrophilic surfaces.

Controllable wettability is important for a wide range of applications, including intelligent switching, self-cleaning and oil/water separation. In this work, rapid switching and extreme wettability changes upon ultraviolet (UV) illumination were investigated. TiO2 nanoparticles were modified in solutions of trimethoxy(alkyl)silane, and the suspensions were sprayed on glass substrates. For such samples, the water contact angle (WCA) was shown to transition from a superhydrophobic (WCA ≈ 165°) to a superhydrophilic (WCA ≈ 0°) state within 10 min upon UV illumination and subsequent recovery to superhydrophobicity occurred after heat treatment. It was found that the changes in the trimethoxy(alkyl)silane upon UV illumination can explain the rapid decrease of the WCA from more than 165° to almost 0°. To further investigate the wettability transition, trimethoxy(alkyl)silane and Al2O3 nanoparticles (which are not photocatalytic) were mixed and spray-coated onto the glass substrates as the control samples. Then the unrecoverable change of trimethoxy(alkyl)silane under UV illumination can be confirmed. It was found that the presence of trimethoxy(alkyl)silane in the TiO2–trimethoxy(alkyl)silane coating served to speed up the super-wettability transition time from superhydrophobicity to superhydrophilicity, but also limited the number of wettability recycle times. With this understanding, the effect of the trimethoxy(alkyl)silane concentration on the number of recycle cycles was investigated.

Photo-Control of Small GTPase RAS using Photo Responsive Peptide Inhibitor Which Mimic αH Helix of SOS

Small GTPase Ras is known as a central regulator of several cellular signaling which are related to cell viability, growth, differentiation and apoptosis. Ras is already studied well at molecular level and they have two state, GTP binding (active) state and GDP-binding (inactive) state. These switching of Ras activity was regulated by two factors, GEFs and GAPs. GEFs serves as Ras activator and they replace GDP from Ras and attach GTP to Ras alternatively. While, GAPs serves as Ras inactivator and they accelerate Ras GTPase. Previously it has been reported that SOSαH mimicking peptide which has cyclic structure at N-terminal region exhibited stablea-helix structure, and inhibit Ras GDP-GTP exchange activity competitively with SOS. In this study, we focused on the interaction between Ras and aH-helix which locates Ras interface of SOS (Ras-GEF) in order to photo-regulate Ras function artificially. Several kinds of αH mimicking peptides which have two cysteine to be crosslinked were synthesized. The cysteine residues of the peptides were crosslinked by bifunctional azobenzene derivatives, azobenzene di-maleimide (ABDM) intramolecularly. The ABDM incorporated into the peptides showed cis-trans isomerization upon ultraviolet (UV) light and visible light irradiations. CD spectral analysis revealed that trans-ABDM-αH peptide forms partially ahelix and cis-ABDM-aH peptide exhibit random secondary structure. SOS dependent GDP-GTP exchange reaction of Ras was inhibited by trans- ABDM-aH peptide. Furthermore, Ex vivo experiment revealed the SOS mimicking peptides exhibit cell membrane permeation indicating the photochromic peptides are applicable to regulation of cell function.

Fabrication, characterization, and luminescent properties of Y2WO6: Gd3+, Dy3+ hierarchical microspheres

A series of monodisperse Y2WO6: Dy3+, Gd3+ hierarchical microspheres were synthesized via a facile surfactant-assisted hydrothermal method followed by heat treatment. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and photoluminescence (PL) spectra. XRD patterns of the samples with Gd3+ codoping exhibit a merging of (− 232) and (232) peaks, indicating the distorted deformation in Y2WO6 host structure. SEM images demonstrate that the Y2WO6: Dy3+, Gd3+ microspheres are well-dispersed and assembled by many irregular nanoparticles. Upon ultraviolet (UV) excitation at 291 nm, the emission peaks of Dy3+ ions is observed at 480 nm (blue), 579 nm (yellow) and 669 nm (red), corresponding to the characteristic transitions of 4F9/2 → 6H15/2, 4F9/2 → 6H13/2 and 4F9/2 → 6H11/2 of Dy3+, respectively. The optimal PL intensity was obtained in Y2WO6: 2.5 mol% Dy3+ microspheres which can be further enhanced with the codoping of Gd3+. The strongest luminescence is achieved at Gd3+ concentration of 40 mol% with a quantum yied (QY) of 34.45%. In addition, the thermal stability of the sample was also investigated. The CIE of the investigated samples exhibit little change by varying the concentration of Gd3+ ions. The calculated CIE values are all around (0.37, 0.38) and located at the white region, suggesting that the Y2WO6: Dy3+, Gd3+ microspheres could be used for white LEDs.

Cytoprotective role of S14G-humanin (HNG) in ultraviolet-B induced epidermal stem cells injury

Skin provides the protective barrier for our body and undergoes the continuous regeneration in order to overcome damage from exposure to harmful environments and wounds. Epidermal stem cells (ESCs) play critical roles in skin regeneration. Humanin analogue, S14G-humanin (HNG), a prominent member of a newly discovered family of mitochondrial-derived peptides, has been shown to be a cytoprotective derivative in multiple cell types. In this study, we isolated mouse epidermal stem cells and investigated the cytoprotective effects of HNG on ESCs upon ultraviolet (UV)-B treatment. We show that HNG suppresses UV-B-induced ROS production and increases antioxidant glutathione expression. HNG-pretreated cells exhibit very mild production of cytokines, including TNF-α, IL-1β, and IL-6, upon exposure to UV-B. HNG pretreatment is protective against UV-B-mediated cytotoxicity and promotes ESC survival. Moreover, HNG treatment attenuates the UV-B-induced reduction in mitochondrial membrane potential (MMP) and preserves their identity and stem cell capacity. Mechanistically, HNG treatment ameliorates the UV-B-induced reduction in Wnt/β-catenin pathway proteins, including Wtn3a, Myc, and cyclin D1. Collectively, our data suggest that HNG acts as a pro-survival and anti-oxidative stress agent in ESCs and has the potential to be used in ESC-mediated therapies.

Photoreactive benzophenone as anchor of modifier to construct durable anti-platelets polymer surface

Surface modification is an effective method to improve the anti-platelets property for blood-contacting biomedical materials. However, for elastomer it is still a challenge to develop a simple and versatile method to preserve desirable property of the modified surface upon repeated deformation. Herein, we synthesized a novel modifier based on the photoreactive benzophenone (BP), which is served as anchor to fix polyethylene glycols (PEG)s onto polymer surface so as to achieve durable anti-platelets surface. Upon ultra-violet (UV) exposure for a very short time, this modifier (BP-PEG) was chemically bonded onto polyurethane (PU) so that its surface property was improved. When increasing the molecular weight or incorporating sulfonate group into BP-PEG, the anti-platelets surface of PU was obtained and this property still could be preserved upon repeated deformation. The universality of this surface modifier was verified by its successful application to the other polymer substrates and improved hydrophilicity. We anticipate this work would pave a new way to construct durable surface with unique property for biomedical devices.

Initial excited state structural dynamics of lumiflavin upon ultraviolet excitation

Excited state photophysics of flavin compounds has attracted great attention due to their involvement in several photobiological processes as a cofactor in photoreceptor enzymes. In this work, we have determined the initial excited state structural dynamics of flavin related compound, lumiflavin (LF), upon ultraviolet (UV) excitation through resonance Raman intensity analysis. A quantitative measurement of resonance Raman cross-sections across the 265 nm absorption band (257–275 nm) of LF have been performed, and Raman excitation profiles (REPs) are constructed for all the Raman active modes. The REPs and absorption cross sections have been simulated using time-dependent wave packet propagation (TDWP) formalism to extract the ultrafast dynamics of LF within 50 fs after photoexcitation. The total internal reorganization energy is estimated to be 470 cm−1, which is clear evidence for the significant structural distortion in the excited state from that of the ground state. By comparing the excited state structural changes between S1 state and 265 nm excited state, we found that different molecular distortions occur following photoexcitation to those two different states. The total reorganization energy is obtained to be 1542 cm−1, in which the maximum contribution comes from the inertial response of water (1070 cm−1). Additionally, our simulation also yields an instantaneous response of the first solvation shell within an ultrafast timescale, τ ∼ 30 fs, following photoexcitation. The current study provides the basis for future investigations to determine the excited state properties of flavin compounds upon UV excitations.

Highly efficient photocontrol of mitotic kinesin Eg5 ATPase activity using a novel photochromic compound composed of two azobenzene derivatives

Mitotic kinesin Eg5 plays an important physiological role in cell division. Several small-molecule inhibitors of Eg5 are the focus of cancer therapies. Azobenzene is a photochromic compound exhibiting cis-trans isomerization upon ultraviolet (UV) and visible (VIS) light irradiation. Photochromic compounds of azobenzene derivatives, mimicking Eg5-specific inhibitors of STLC, indicated photoreversible inhibitory effects on Eg5 ATPase activity; however, the photoreversible switching efficiency was not significant. This study presents a novel synthesized photochromic Eg5 inhibitor 2, 3-bis[(2,5-dioxo-1-{4-[(E)-2-phenyldiazen-1-yl]phenyl}pyrrolidin-3-yl)sulfanyl] butanedioic acid (BDPSB), which is composed of two azobenzenes. BDPSB exhibited cis-trans isomerization with UV and VIS light irradiation. The trans form of BDPSB significantly inhibited microtubule-dependent ATPase activity of Eg5, with an IC50 of 74 μM. Cis BDPSB showed weak effects on the microtubule-dependent ATPase activity. The results suggest that the novel photochromic Eg5 inhibitor BDPSB, which exhibits highly efficient photoswitching, shows a switch 'ON' and 'OFF' behaviour with VIS and UV light irradiation.

Drug photoallergy

AbstractDrugs are one of the representative exogenous agents that cause photosensitive dermatitis. Both phototoxic and photoallergic mechanisms exist in photosensitivity to exogenous agents. While the phototoxic reaction is mediated mainly by reactive oxygen species, the photoallergic reaction is induced and elicited by immunological consequences. Two hypotheses have been put forward to explain the formation of photoallergen: prohapten and photohapten. The vast majority of clinically photoallergic drugs are photohapten rather than prohapten. Clinically, photocontact dermatitis and drug photosensitivity are the two major disorders caused by topical and systemic exogenous photosensitizers, respectively. The main cause of photocontact dermatitis is nonsteroidal anti‐inflammatory drugs. In drug photosensitivity, various causative agents have been reported and are recently represented by hydrochlorothiazide, quinolones, piroxicam, and flutamide. Orally administered drugs diffuse from the blood to the epidermis, and keratinocytes are photoderivatized with a given drug upon ultraviolet (UV) A irradiation, leading to photoantigen formation and cytokine production. In parallel, dendritic cells become photohapten‐bearing, T‐cell–sensitizing cells. Considering the mechanisms of photoallergy to chemicals, several in vitro assessments have been proposed to detect the photoallergenicity. Finally, a recent observation with newly marketed drugs has demonstrated that drugs may function as immunomodulators and induce photosensitivity as typically seen in anti‐CCR4 antibody.

Facile Synthesis and Down-Conversion Emission of RE3+-Doped Lutetium Oxide Nanoparticles.

Lu2O3:RE3+ (RE3+ = Eu3+, Tb3+, Ho3+) nanoparticles have been successfully synthesized by a facile homogeneous precipitation method with subsequent sintering process. The crystal structure, morphology and luminescence properties of the as-prepared samples have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), photoluminescence (PL) and cathodoluminescence (CL) spectra. Upon ultraviolet (UV) and low-voltage electron beam excitation, Lu2O3:RE3+ (RE3+ = Eu3+, Tb3+, Ho3+) nanoparticles show strong red (Eu3+,5D0 → 7F2), green (Tb3+,5D4 → 7F5), and green (Ho3+,5S2 → 5I8) emissions. They exhibit a good advantage of multicolor emissions in the visible region, and endow these kinds of materials with potential application in many fields, such as light display systems, optoelectronic devices and biological imaging.

Photo-triggered micelles: simultaneous activation and release of microtubule inhibitors for on-demand chemotherapy.

The nonspecific biodistribution of cytotoxic drugs and associated adverse effects greatly limit the efficacy and patient compliance of chemotherapy. To address this, we employed a photoswitchable microtubule inhibitor (Azo-CA4) that was physically loaded in cyclodextrin-bearing micellar nanocarriers through the host-guest interaction. Azo-CA4 was only activated upon ultraviolet (UV) light irradiation to trigger the transition from the "trans" (inactive) to "cis" (active) state. Such conformation change could then induce rapid Azo-CA4 release from micelles without the delay of the onset of therapeutic action. This nanoscale delivery system produced photo-triggered antimitotic and pro-apoptotic effects in MDA-MB-231 cells via a triggered control of microtubule dynamics. The anticancer efficacy of Azo-CA4-loaded micelles was further proved in vivo using a 4T1 tumor-bearing mice model coupled with multiple topical administrations to avoid the penetration problem of UV light. This work provides a new delivery vehicle to aid the application and potential translation of Azo-CA4 as biomedical tools and precision chemotherapeutics.

Ferrite Paste Cured With Ultraviolet Light for Additive Manufacturing of Magnetic Components for Power Electronics

Additive manufacturing (AM) has the potential to rapidly prototype innovative designs of magnetic components aimed at improving power density and efficiency of switch-mode power converters. However, only a few magnetic feedstocks are available for AM, and the fabricated parts have significantly poorer magnetic properties. Our previous studies showed the promise of an extrusion-based AM platform for making high-performance power magnetics. But, the magnetic paste feedstock developed in these studies suffered from the “slumping” problem, thus not suitable for building large or tall core structures. To improve the AM capability, a ferrite paste was developed that is cured upon ultraviolet (UV) illumination. Core structures with large aspect ratios were fabricated by retrofitting the printer with a UV-light-emitting diode module. By varying the magnetic composition of the paste and sintering the printed parts at and below 1000 °C, we made tall (>4 mm) ferrite cores with relative permeability ranging from 63 to 103 and resonance frequency higher than 30 MHz.

Photocatalytic and Photoluminescence Properties of Core–Shell SiO2@TiO2:Eu3+,Sm3+ and Its Etching Products

A novel multifunctional core–shell, yolk–shell SiO2@TiO2:Eu3+/Sm3+ and hollow TiO2:Eu3+/Sm3+ structures were successfully synthesized. The relationship between morphology/ions doping and multifunctional properties including photoluminescence and photocatalysis has been discussed in detail for the first time using systematic characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL), ultraviolet–visible light (UV-vis) analysis, Fourier transform infrared (FT-IR) spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis, and X-ray photoelectron spectroscopy (XPS). Upon ultraviolet (UV) excitation, the products show the characteristic red and orange–red emission lines of Eu3+ and Sm3+, respectively. In addition, Judd–Ofelt intensity parameters (Ω2, Ω4) were used to investigate the symmetry and coordination state of Eu3+ ions in the products with different morphologies. The relative luminescence inte...

μPAD Fluorescence Scattering Immunoagglutination Assay for Cancer Biomarkers from Blood and Serum.

A microfluidic paper analytical device (μPAD) was created for the sensitive quantification of cancer antigens, carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA 19-9), from human whole blood and serum, toward diagnosis and prognosis of colorectal cancer. Anti-CEA and anti-CA 19-9 antibodies were covalently linked to submicron, fluorescent polystyrene particles, loaded, and then dried in the center of the μPAD channel. CEA- or CA 19-9-spiked blood or serum samples were loaded to the inlet of μPAD, and subsequent immunoagglutination changed the fluorescent scatter signals upon ultraviolet (UV) excitation. The total assay time was about 1 min. Detection limits were 1 pg/mL for CEA and 0.1 U/mL for CA 19-9 from both 10% diluted blood and undiluted serum. The use of UV excitation and subsequent fluorescence scattering enabled much higher double-normalized intensities (up to 1.28-3.51, compared with 1.067 with the elastic Mie scatter detection), successful detection in the presence of blood or serum, and distinct multiplex assays with minimum cross-reaction of antibodies. The results with undiluted serum showed the larger dynamic range and smaller standard errors, which can be attributed to the presence of serum proteins, functioning as a stabilizer or a passivating protein for the particles within paper fibers.

Structure and color-tunable luminescence properties of Ce3+ and Tb3+-activated Mg2La8(SiO4)6O2 phosphors based on energy transfer behavior

A series of novel luminescent emission-tunable phosphors Mg2La8(SiO4)6O2:Ce3+,Tb3+ (MLS:Ce3+,Tb3+) have been prepared by a solid-state reaction. The phase formation was firstly confirmed through X-ray diffraction technique and refined by the Rietveld method. The MLS:Ce3+,Tb3+ phosphors, which crystallized in apatite-type hexagonal phase, exhibited a broad excitation band ranging from 200 to 400nm and several emission bands centered at 426nm and 551nm. Energy transfer from Ce3+ to Tb3+ ions via a dipole-dipole mechanism occurred in the as-synthesized phosphors upon ultraviolet (UV) excitation. The energy transfer efficiency increases with increasing doping content of Tb3+ ions, which was confirmed by the luminescence spectra and fluorescence decay curves of corresponding ions simultaneously. The energy transfer critical distance was calculated and evaluated by both the concentration quenching and spectral overlap methods. The chromaticity of emission-tunable phosphors was also characterized by the Commission International de l'éclairage (CIE) chromaticity indexes, and the color tone can be tuned from blue (0.179, 0.122) to green (0.267, 0.408) by controlling the ratio of Ce3+/Tb3+.

Strong UV Emission from Colloidal Eu2+‐Doped BaSO4 Nanoparticles: A Material for Enhancing the Photocatalytic Activity of Carbon Dots

AbstractIn this article, we report a facile microwave‐assisted green synthetic route for the preparation of highly luminescent water dispersible polyacrylic acid‐coated europium (Eu2+)‐doped BaSO4 nanoparticles at low temperature for the first time. Polyacrylic acid coating over nanoparticles renders them water dispersible. Upon ultraviolet (UV) (250 nm) excitation, europium‐doped BaSO4 nanoparticles exhibit a strong and broad UV luminescence near at 368 nm. This emission peak is quite strong and has a relative luminescence quantum yield (QY) of 53 %. The high QY of the UV emission from the nanoparticles is explored for the enhancement of the visible photocatalytic properties of the carbon dots (Cdots). In fact, faster degradation of the Rhodamine B is noted for the mixture containing both Eu2+‐doped BaSO4 nanoparticles and cetyl trimethylamonium bromide capped carbon dots. This is attributed to the strong overlap of the UV emission of Eu2+ with the absorption spectrum of Cdots leading to high energy transfer efficiency (∼64 %). The energy transfer process is supported by the observation of lower dye degradation for the diluted colloidal mixtures where the average distance between Eu2+ in BaSO4 to Cdots nanoparticles is increased.

Investigation on the preparation and luminescence property of (Gd1−Dy )2O3 (x=0.01–0.10) spherical phosphors

Abstract Uniform spheres of (Gd 1− x Dy x ) 2 O 3 ( x =0.01–0.10) have been converted from their colloidal precursor spheres synthesized via homogeneous precipitation. The synthesis, particle size control, luminescent properties and energy transfer of the (Gd 1 -x Dy x ) 2 O 3 were systematically studied by the combined techniques of fourier transform infrared (FT-IR) spectroscopy, x-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence excitation/ photoluminescence (PLE/PL) spectroscopy, and fluorescence decay analysis. The precursor exhibit mono-dispersed spherical morphology and its size can be efficiently controlled by adjusting the urea content. The phase pure (Gd 1− x Dy x ) 2 O 3 oxides can be obtained by calcining precursor at 600 °C, and the spherical morphology remained at even high temperature of 1000 °C. The (Gd 1− x Dy x ) 2 O 3 phosphors display strong yellow emission at 575 nm ( 4 F 9/2 → 6 H 13/2 transition of Dy 3+ ) and weak blue emission at 486 nm ( 4 F 9/2 → 6 H 15/2 transition of Dy 3+ ) upon ultraviolet (UV) excitation of Gd 3+ at 275 nm ( 8 S 7/2 → 6 I J transition of Gd 3+ ). The optimal content of Dy 3+ was found to be ~2 at% ( x =0.02) due to the concentration quenching. Owing to the efficient Gd 3+ →Dy 3+ energy transfer, the fluorescent property of the phosphor was significantly improved. The emission intensity of (Gd 1− x Dy x ) 2 O 3 increased with calcination temperature and particle size increasing, while the lifetime for the 575 nm emission gradually decreased. The (Gd 1− x Dy x ) 2 O 3 spheres developed in the present work is expected to be a promising yellow phosphor widely used in the lighting and display areas.

Synthesis and properties of photochromic spirooxazine with aggregation-induced emission fluorophores polymeric nanoparticles

We designed and synthesized photochromic fluorescent poly (MMA-co-SPO-co-TPE) nanoparticles with pendant spirooxazine (SPO) dye and tetraphenylethylene (TPE) fuorophores attached to poly (methyl methacrylate) (MMA) backbone by semi-continuous polymerization. The polymerization reactions were accomplished in water with randomly methylated-β-cyclodextrin (β-CD) at 80 °C in the presence of potassium peroxodisulfate which can be used as free radical initiator. This new synthetic method leads to uniform and smooth nanoparticles with a narrow particle size distribution. In addition, the poly (MMA-co-SPO-co-TPE) nanoparticles exhibit aggregation induced emission (AIE) properties and excellent photochemical properties because of spirooxazine dyes convert reversibly to merocyanine form upon ultraviolet (UV) irradiation, which active the intramolecular energy transfer pathway and quench the fluorescence of TPE in polymers. Consequently, the fluorescence of the poly (MMA-co-SPO-co-TPE) nanoparticles can be reversibly switched “on” and “off” upon UV and visible light, which maybe have potential application in biological fluorescent labeling as well as in optical fields like individually light–addressable nanoscale devices.

Synthesis, Crystal Structure, Magnetic Property and Photo-Induced Coloration of a One-Dimensional Chain Complex

A novel photoactive complex was constructed from two non-photoactive ligands and cobalt (II) ions. Upon ultra violet (UV) irradiation (365 nm), the color of complex 1 changes from orange to violet. The ESR spectrum indicates that the photoactive phenomenon of complex 1 originates from an intermolecular energy transfer between the H5DDCPBA ligand and phenanthroline ligand. This photoactive complex shows high thermal stability according to the investigation of thermogravimetric analyses. In addition, the temperature dependence of magnetic susceptibilities for the orange complex 1 was also investigated systematically.

Enhanced Release of Molecules upon Ultraviolet (UV) Light Irradiation from Photoresponsive Hydrogels Prepared from Bifunctional Azobenzene and Four-Arm Poly(ethylene glycol).

Advances in biosensors and drug delivery are dependent on hydrogels that respond to external stimuli. In this work, we describe the preparation and characterization of photoresponsive hydrogels prepared by cross-linking of di-NHS ester of azobenzoic acid and four-armed, amine-terminated poly(ethylene glycol). The porous structure and composition of the hydrogels were confirmed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The reversible photoisomerization of the azobenzene-containing hydrogel cross-linkers in the gels was confirmed by absorption spectroscopy. Specifically, the photoisomerization of the cross-linkers between their trans and cis configurations was observed by monitoring the absorbance of the hydrogels at the two characteristic peaks of azobenzene (π-π* at 330 nm and n-π* at 435 nm). The effect of photoisomerization on the hydrogel structure was investigated by microscopy. Ultraviolet (UV) irradiation-induced reduction in hydrogel size was observed, which may be a result of the inherently smaller footprint of the cis azobenzene conformation, as well as dipole-dipole interactions between the polar cis azobenzene and the polymer network. The UV-triggered reduction in hydrogel size was accompanied by enhanced release of the near-infrared fluorescent dye Alexa Fluor 750 (AF750). Enhanced release of AF750 was observed in samples irradiated with UV versus dark control. Together, these data demonstrate the potential of these systems as reversible photoresponsive biomaterials.

Nonlinear imaging microscopy for assessing structural and photochemical modifications upon laser removal of dammar varnish on photosensitive substrates.

The nonlinear optical microscopy (NLM) modalities of Multi-Photon Excited Fluorescence (MPEF) and Third Harmonic Generation (THG) have been combined in this work to characterize as a function of depth with micrometric resolution the type and extent of morphological and photochemical modifications that take place upon ultraviolet (UV) pulsed laser removal of a dammar varnish layer applied on a photosensitive substrate. The latter consists on a layer of the synthetic polymer poly-methyl methacrylate doped with a photosensitizer, the aromatic compound 1,4-di[2-(5-phenyloxazolyl)] benzene, that strongly fluoresces upon UV light illumination. A number of laser conditions for partial or total elimination of the varnish coating were explored, namely different wavelengths (266, 248 and 213 nm) and pulse durations, in the nanosecond, picosecond and femtosecond ranges. Changes in the MPEF signals upon laser ablation of the outermost varnish layer successfully signpost photochemical modifications of the varnish or of the photosensitive under-layer, and their dependence with the laser ablation parameters, i.e., wavelength and pulse duration. In turn, THG signals mark the presence of layer boundaries and the reduction by laser ablation of the thickness of the varnish coating. The obtained MPEF and THG data are complemented by morphological observation by optical microscopy and measurements of laser induced fluorescence and micro-Raman spectra of the samples before and after laser ablation at the selected laser irradiation conditions. The results acquired through these non-destructive NLM imaging techniques serve to understand the phenomena that are induced upon laser ablation and to determine the best operating conditions that ensure controlled removal of the varnish with minimal morphological and chemical modifications to the under-layers. This research is of direct application to the UV pulsed laser cleaning of paintings and demonstrates the potential of NLM as a novel assessment tool for non-destructive, on line monitoring of the laser cleaning process.