Femtosecond Laser Illumination Research Articles

Ambient black carbon particles in human ovarian tissue and follicular fluid

Evidence indicates a link between exposure to ambient air pollution and decreased female fertility. The ability of air pollution particles to reach human ovarian tissue and follicles containing the oocytes in various maturation stages has not been studied before. Particulate translocation might be an essential step in explaining reproductive toxicity and assessing associated risks. Here, we analysed the presence of ambient black carbon particles in (i) follicular fluid samples collected during ovum pick-up from 20 women who underwent assisted reproductive technology treatment and (ii) adult human ovarian tissue from 5 individuals. Follicular fluid and ovarian tissue samples were screened for the presence of black carbon particles from ambient air pollution using white light generation by carbonaceous particles under femtosecond pulsed laser illumination. We detected black carbon particles in all follicular fluid (n = 20) and ovarian tissue (n = 5) samples. Black carbon particles from ambient air pollution can reach the ovaries and follicular fluid, directly exposing the ovarian reserve and maturing oocytes. Considering the known link between air pollution and decreased fertility, the impact of such exposure on oocyte quality, ovarian ageing and fertility needs to be clarified urgently.

Femtosecond-laser-inscribed Bragg grating in hollow-core fiber for highly sensitive optofluidic sensing.

An optofluidic sensor based on a Bragg grating in hollow-core fiber (HCF) is experimentally demonstrated. The grating is inscribed into the HCF by femtosecond laser illumination through a phase mask. Periodic index modulation is introduced into the silica material surrounding the hollow core, causing cladding mode resonance, and multiple reflection peaks are observed in the grating spectrum. These reflection peaks later shift to longer wavelengths when high-index liquid is infiltrated into the HCF. The new reflection peak results from the backward coupling of the liquid core mode of the waveguide, the mode field of which overlaps with the grating modulation surrounding the liquid core. The resonant wavelength of the liquid-core fiber grating increases with the index value of the infiltrating liquid, and optofluidic refractive index sensing is realized with the device. The highest refractive index sensitivity, 1117 nm/RIU, is obtained experimentally in the index range of 1.476-1.54. The infiltrated hollow-core fiber Bragg grating also exhibits high temperature sensitivity due to the high thermal-optic coefficient of the liquid, and a sensitivity of -301 pm/°C is achieved in the temperature range of 25°C to 60°C.

Enhancing THz emission from nonlinear metasurfaces by a Bragg perfect absorber.

Nonlinear plasmonic metasurfaces were demonstrated recently as ultracompact tetrahertz (THz) sources, emitting relatively strong single-cycle THz pulses after femtosecond laser illumination. There has been great progress in their ability to generate controlled THz wavepackets; however, their overall emission strength has not yet been optimized. Here we numerically show that by designing a Bragg assisted perfect absorber we can improve the coupling of the pumping laser to the nonlinear metasurface. This results in over an order of magnitude enhancement of the THz signal. Moreover, we show that this method can be combined with other independent optimization schemes to further enhance the radiated THz, reaching over two orders of magnitude emission enhancement compared with previously studied plasmonic metasurfaces.

34 Placental-Fetal Distribution of Carbon Particles in a Pregnant Rabbit Model After Repeated Exposure to Diluted Diesel Engine Exhaust

Abstract Airborne pollution particles have been shown to translocate from the mother’s lung to the fetal circulation but their placental-fetal distribution and internal tissue load remain poorly explored. Here, we investigated the placental-fetal distribution of diesel engine exhaust particles during gestation under controlled exposure conditions using a pregnant rabbit model. Pregnant dams were exposed by nose-only inhalation to either clean air (controls) or diluted and filtered diesel engine exhaust (1 mg/m3) for 2h/day, 5 days/week, from gestational day (GD) 3 to GD27. At GD28, placental and fetal tissues (i.e., heart, kidney, liver, lung and gonads) were collected for biometry and to study the accumulation of carbon particles (CPs) using white light generation by carbon particles under femtosecond pulsed laser illumination. CPs were detected in the placenta, fetal heart, kidney, liver, lung and gonads in significantly higher amounts compared with controls. By using multiple factor analysis, we were able to discriminate the diesel engine-exposed pregnant rabbits from the control group taking all variables related to fetoplacental biometry and CP load into consideration. Although our findings did not reveal a sex effect, a potential interaction effect might be present between exposure and fetal sex. The results confirm the translocation of maternally inhaled CPs from diesel engine exhaust to the placenta and the ability to reach fetal organs during late-stage pregnancy. The differential particle load in the fetal organs may contribute to the disruption of blood flow in the placenta with possible effects on fetoplacental biometry and placental function.

Accumulation of Black Carbon Particles in Placenta, Cord Blood, and Childhood Urine in Association with the Intestinal Microbiome Diversity and Composition in Four- to Six-Year-Old Children in the ENVIRONAGE Birth Cohort.

The gut microbiome plays an essential role in human health. Despite the link between air pollution exposure and various diseases, its association with the gut microbiome during susceptible life periods remains scarce. In this study, we examined the association between black carbon particles quantified in prenatal and postnatal biological matrices and bacterial richness and diversity measures, and bacterial families. A total of 85 stool samples were collected from 4- to 6-y-old children enrolled in the ENVIRonmental influence ON early AGEing birth cohort. We performed 16S rRNA gene sequencing to calculate bacterial richness and diversity indices (Chao1 richness, Shannon diversity, and Simpson diversity) and the relative abundance of bacterial families. Black carbon particles were quantified via white light generation under femtosecond pulsed laser illumination in placental tissue and cord blood, employed as prenatal exposure biomarkers, and in urine, used as a post-natal exposure biomarker. We used robust multivariable-adjusted linear models to examine the associations between quantified black carbon loads and measures of richness (Chao1 index) and diversity (Shannon and Simpson indices), adjusting for parity, season of delivery, sequencing batch, age, sex, weight and height of the child, and maternal education. Additionally, we performed a differential relative abundance analysis of bacterial families with a correction for sampling fraction bias. Results are expressed as percentage difference for a doubling in black carbon loads with 95% confidence interval (CI). Two diversity indices were negatively associated with placental black carbon [Shannon: (95% CI: , ); Simpson: (95% CI: , )], cord blood black carbon [Shannon: (95% CI: , ); Simpson: (95% CI: , )], and urinary black carbon [Shannon: (95% CI: , ); Simpson: (95% CI: , )]. The explained variance of black carbon on the above indices varied from 6.1% to 16.6%. No statistically significant associations were found between black carbon load and the Chao1 richness index. After multiple testing correction, placental black carbon was negatively associated with relative abundance of the bacterial families Defluviitaleaceae and Marinifilaceae, and urinary black carbon with Christensenellaceae and Coriobacteriaceae; associations with cord blood black carbon were not statistically significant after correction. Black carbon particles quantified in prenatal and postnatal biological matrices were associated with the composition and diversity of the childhood intestinal microbiome. These findings address the influential role of exposure to air pollution during pregnancy and early life in human health. https://doi.org/10.1289/EHP11257.

Association of urinary and ambient black carbon, and other ambient air pollutants with risk of prediabetes and metabolic syndrome in children and adolescents

The effects of exposure to black carbon (BC) on various diseases remains unclear, one reason being potential exposure misclassification following modelling of ambient air pollution levels. Urinary BC particles may be a more precise measure to analyze the health effects of BC. We aimed to assess the risk of prediabetes and metabolic syndrome (MetS) in relation to urinary BC particles and ambient BC and to compare their associations in 5453 children from IDEFICS/I. Family cohort. We determined the amount of BC particles in urine using label-free white-light generation under femtosecond pulsed laser illumination. We assessed annual exposure to ambient air pollutants (BC, PM2.5 and NO2) at the place of residence using land use regression models for Europe, and we calculated the residential distance to major roads (≤250 m vs. more). We analyzed the cross-sectional relationships between urinary BC and air pollutants (BC, PM2.5 and NO2) and distance to roads, and the associations of all these variables to the risk of prediabetes and MetS, using logistic and linear regression models. Though we did not observe associations between urinary and ambient BC in overall analysis, we observed a positive association between urinary and ambient BC levels in boys and in children living ≤250 m to a major road compared to those living >250 m away from a major road. We observed a positive association between log-transformed urinary BC particles and MetS (ORper unit increase = 1.72, 95% CI = 1.21; 2.45). An association between ambient BC and MetS was only observed in children living closer to a major road. Our findings suggest that exposure to BC (ambient and biomarker) may contribute to the risk of MetS in children. By measuring the internal dose, the BC particles in urine may have additionally captured non-residential sources and reduced exposure misclassification. Larger studies, with longitudinal design including measurement of urinary BC at multiple time-points are warranted to confirm our findings.

Rapid, noncontact, sensitive, and semiquantitative characterization of buffered hydrogen-fluoride-treated silicon wafer surfaces by terahertz emission spectroscopy

Advances in modern semiconductor integrated circuits have always demanded faster and more sensitive analytical methods on a large-scale wafer. The surface of wafers is fundamentally essential to start building circuits, and quantitative measures of the surface potential, defects, contamination, passivation quality, and uniformity are subject to inspection. The present study provides a new approach to access those by means of terahertz (THz) emission spectroscopy. Upon femtosecond laser illumination, THz radiation, which is sensitive to the surface electric fields of the wafer, is generated. Here, we systematically research the THz emission properties of silicon surfaces under different surface conditions, such as the initial surface with a native oxide layer, a fluorine-terminated surface, and a hydrogen-terminated surface. Meanwhile, a strong doping concentration dependence of the THz emission amplitude from the silicon surface has been revealed in different surface conditions, which implies a semiquantitative connection between the THz emission and the surface band bending with the surface dipoles. Laser-induced THz emission spectroscopy is a promising method for evaluating local surface properties on a wafer scale.

COVID-19 disease severity in hospitalized patients is associated with short- and long-term exposure to air pollutants

Background and Aim Existing evidence suggests that exposure to air pollutants (AP) such as particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2) and black carbon (BC) is associated with COVID-19 infection rates and mortality. We investigated whether exposure to AP was associated with COVID-19 disease severity in a cohort of hospitalised COVID-19 patients. Methods 329 COVID-19 patients were recruited at the time of admission to hospital. Clinical parameters and outcomes were collected from medical records, including the duration of stay, the early-warning score (EWS), oxygen saturation, and PaO2/FiO2 ratios. Daily exposure levels for PM2.5, PM10, NO2 and BC were modelled using a high-resolution spatiotemporal model. Black carbon particles in blood were quantified using femtosecond pulsed laser illumination. Associations between exposure to air pollutants and clinical outcomes were modelled using multiple regression models while adjusting for potential confounders. Results The duration of stay increased by 1 to 6 days for an interquartile range (IQR) increase in average exposure to AP in the week before admission (PM2.5: +5.2 days, NO2: +5.8 days). Similarly, an IQR increase in long-term exposure (to AP was associated with increased duration of stay (PM2.5: +2.8 days, NO2: +3.2 days, BC: +2.8 days). Furthermore, an increase in PM2.5 exposure 1 week before admission was associated with higher EWS (+0.40). Finally, IQR increases in long-term exposure to PM10, BC and NO2 as well as blood black carbon load were associated with odds of admission to the intensive care unit (OR: +1.32, +2.12, +2.46 and +1.19 respectively). Conclusion Exposure to AP was associated with duration of stay and EWS scores at the time of admission, which implies a potential link between AP exposure and COVID-19 disease severity, and a significant influence of AP exposure on the pressure on medical care systems during the COVID-19 pandemic.

Ambient exposure and fetal black carbon load in association with telomere length in cord blood

Background: Ambient particulate matter (PM) is an important factor that is associated with telomere length (TL) at birth. A recent study has shown that translocation of black carbon (BC), one of the most toxic components of PM, towards the fetus is possible, but it is not yet linked to biological outcomes. In this study, we investigated whether 1) ambient BC is associated with cord blood TL, 2) fetal BC load relates to ambient BC exposure and 3) fetal BC load is related to newborn TL. Methods: In 247 mother-newborn pairs from the ENVIRONAGE (Environmental Influence On Early Ageing) study, which is a population-based birth cohort study located in Limburg, Belgium, maternal residential exposure to BC during pregnancy was estimated using a spatial-temporal interpolation model. BC particles were detected in cord blood by the generation of white-light under femtosecond pulsed laser illumination. Cord blood TL was measured using qPCR. We applied Pearson correlations and distributed lag models to associate BC exposure with cord blood TL. Results: An IQR increment (0.85 µg/m3) in ambient BC was associated with a -12% (95% CI: −21% to −2.8%) decrease and a 20% (95% CI: 7.6% to 34%) increase in cord blood TL during the second and third trimester of pregnancy respectively. Secondly, fetal BC load showed the highest correlation with ambient BC during trimester 3 (r=0.28, p<0.0001). Thirdly, fetal BC load was positively correlated with TL in cord blood (r=0.15, p=0.023). Conclusion: Our findings show that mothers with a higher exposure to ambient BC had more BC particles in cord blood. The positive correlation between both ambient and fetal BC exposure during trimester 3 and cord blood TL may suggest the possibility of an acute protective response, but additional studies are needed to investigate the underlying mechanisms. Keywords: Telomere Length, Particulate Matter, Black Carbon, Ageing

Probing neuronal functions with precise and targeted laser ablation in the living cortex: reply

In their comment on Optica 8, 1559 (2021)OPTIC82334-253610.1364/OPTICA.433562, Liang and Vogel performed a theoretical calculation to show that with a 1.1 NA objective and 140 femtosecond (fs) laser pulses with a single pulse energy of 2.2 nJ and 80 MHz repetition rate, the focal point temperature rises 0.3 K and reaches equilibrium after 100 µs in water [Optica 9, 868 (2022)OPTIC82334-253610.1364/OPTICA.454469]. They suggest that the damage to brain tissue by laser could not be caused by thermal effects but rather by plasma-mediated chemical effects. To quantify the thermal accumulation due to the femtosecond (fs) laser illumination in living animals, we used a thermocouple sensor to measure the temperature change in the vicinity of the laser focus at a depth of 300 µm in the cortex of an adult mouse. Our results show that laser irradiation at 930 nm wavelengths with power ranging from 19 to 300 mW can all lead to a brain tissue temperature rise of more than 0.3 K at 1 s at a distance of 25 µm from the laser focus, and the 300 mW laser can cause a temperature increase of more than 28 K at 6 s. These experimental measurements are significantly higher than theoretically calculated values in the comment. These results suggest that the thermal accumulation effect of focused low-energy pulses from fs laser oscillators could contribute significantly to the collateral damage in the living brain.

Two-photon photoluminescence and bio-imaging application of monodispersed perovskite-in-silica nanocrystals with high biocompatibility

• The application of CsPbBr 3 @SiO 2 NCs in two-photon bioimaging was studied for the first time. • CsPbBr 3 @SiO 2 NCs show strong two-photon photoluminescence and good biocompatibility. • SiO 2 shell with optimal thickness can control leakage of Pb 2+ and enhance photoluminescence. Developing two-photon photoluminescence bio-probes with high-biocompatibility is still a challenge. In this work, single CsPbBr 3 perovskite NCs were encapsulated into a silica nanoshell to prevent leakage of Pb 2+ ion out of the shell, and their two- and one-photon photoluminescence property, as well as the application potential for bio-imaging, were investigated by detailed optical characterization and two-photon cell imaging experiment. It turns out that the core–shell NCs show good two-photon absorption property under the excitation of an 800 nm femtosecond laser and emit green light peaked at 526 nm. The survival rate of human hepatocellular carcinomas (HepG2) cells maintains 96.21% after incubating with the core–shell NCs (16 μg/mL) for 24 h without adding protective ligands, demonstrating the excellent biocompatibility of the nanoprobes. Based on the excellent biocompatibility and good two-photon absorption property of the perovskite-in-silica nanoprobes, fluorescence imaging of HepG2 cells was demonstrated under 800 nm femtosecond laser illumination. The cumulative fluorescence intensity of the two-photon fluorescence images was five times higher than the control group. This work demonstrates the good two-photon photoluminescence property of well-controlled core–shell perovskite-in-silica NCs and provides a new insight for the promising applications in bio-imaging.

Morphology and statistics of wide-spectrum speckles.

Although the theory of scattered speckles was initially established via idealization of treating the incident light as monochromatic, phenomenon and regulations of wide-spectrum speckles are yet urgent to be studied, with immense growing applications of broadband source such as femtosecond laser, light-emitting-diode and sunlight illumination. Here we quantitatively analyze the morphology and statistics of speckles produced by a point-like source with wide-spectrum, using a phase plate model to describe the scattering layer. Due to differences in induced phase related to wavelength, wide-spectrum speckle patterns appear radial divergence in intensity distribution, as well as in visibility of both speckles and that of the second-order coherence. This is significantly different from the translation-invariance of monochromatic speckles. The spatially-varying morphology and statistics of the speckles contain spatial and spectral information of the incidence, thus can be used as an indicator to achieve optical metrology or sensing with a wide-spectrum source in the scattering environment.

A better understanding of terahertz emission from semiconductor surfaces with a phased-array effect

We studied the phased-array effects in terahertz emission from semiconductor surfaces upon femtosecond laser illumination. A finite-difference time-domain simulation and experimental observation of the radiation patterns were utilized to examine the optical excitation at normal to the semiconductor surface and oblique angles of 30° and 45° with diameters of ∼10 and 275 μm. The results revealed that there exists a clear phased-array effect for the defocusing conditions. The larger diameter induced a pronounced directivity of the emission owing to the constructive interference of multiple point sources obeying the law of linear superposition, whereas the radiation patterns at smaller diameters were explained as the dipole point source. This finding, in addition to previous studies, will provide a better understanding and contribute to applications of terahertz emission spectroscopy in the field of semiconductor research and development.

Label-free detection of uptake, accumulation, and translocation of diesel exhaust particles in ex vivo perfused human placenta

BackgroundPregnant women and developing fetuses comprise a particularly vulnerable population as multiple studies have shown associations between prenatal air pollution exposure and adverse pregnancy outcomes. However, the mechanisms underlying the observed developmental toxicity are mostly unknown, in particular, if pollution particles can cross the human placenta to reach the fetal circulation.ResultsHere, we investigated the accumulation and translocation of diesel exhaust particles (DEPs), as a model particle for combustion-derived pollution, in human perfused placentae using label-free detection by femtosecond pulsed laser illumination. The results do not reveal a significant particle transfer across term placentae within 6 h of perfusion. However, DEPs accumulate in placental tissue, especially in the syncytiotrophoblast layer that mediates a wealth of essential functions to support and maintain a successful pregnancy. Furthermore, DEPs are found in placental macrophages and fetal endothelial cells, showing that some particles can overcome the syncytiotrophoblasts to reach the fetal capillaries. Few particles are also observed inside fetal microvessels.ConclusionsOverall, we show that DEPs accumulate in key cell types of the placental tissue and can cross the human placenta, although in limited amounts. These findings are crucial for risk assessment and protection of pregnant women and highlight the urgent need for further research on the direct and indirect placenta-mediated developmental toxicity of ambient particulates.

Terahertz Emission Spectroscopy and Microscopy on Ultrawide Bandgap Semiconductor β-Ga2O3

Although gallium oxide Ga2O3 is attracting much attention as a next-generation ultrawide bandgap semiconductor for various applications, it needs further optical characterization to support its use in higher-performance devices. In the present study, terahertz (THz) emission spectroscopy (TES) and laser THz emission microscopy (LTEM) are applied to Sn-doped, unintentionally doped, and Fe-doped β-Ga2O3 wafers. Femtosecond (fs) laser illumination generated THz waves based on the time derivative of the photocurrent. TES probes the motion of ultrafast photocarriers that are excited into a conduction band, and LTEM visualizes their local spatiotemporal movement at a spatial and temporal resolution of laser beam diameter and a few hundred fs. In contrast, one observes neither photoluminescence nor distinguishable optical absorption for a band-to-band transition for Ga2O3. TES/LTEM thus provides complementary information on, for example, the local mobility, surface potential, defects, band bending, and anisotropic photo-response in a noncontact, nondestructive manner. The results indicated that the band bends downward at the surface of an Fe-doped wafer, unlike with an n-type wafer, and the THz emission intensity is qualitatively proportional to the product of local electron mobility and diffusion potential, and is inversely proportional to penetration depth, all of which have a strong correlation with the quality of the materials and defects/impurities in them.

Ambient PM particles reach mouse brain, generate ultrastructural hallmarks of neuroinflammation, and stimulate amyloid deposition, tangles, and plaque formation

Mice were exposed to ambient PM particles 8 h per day, 6 days per week, for twenty-four weeks in enrichment chambers, with real-time mass concentration of PM2.5 around 70 µg/m3, and the number of PM0.1 about 10,000-20,000/m3. The component analysis of PM particles by inductive coupled plasma emission spectrometer detected low concentrations of species associated with crustal materials, metalloid, transition metals, and heavy metals originating from industrial emission. High-performance liquid chromatography (HPLC) detected 22 polycyclic aromatic hydrocarbons originating from traffic exhausts. We found that PM particles from dirty air entered mouse brain which were visualized by field emission scanning electron microscopy (FE-SEM) and were counted by femtosecond pulsed laser illumination microscopy. FE-SEM of brain tissues from dirty air (n=8), and filtered air (control) (n=8) revealed ultrastructural hallmarks of neuroinflammation, enlarged perivascular space, and the attachment of inflammatory cells to the endothelium of blood vessels in brain. Exposure to dirty air containing ambient PM particles resulted in amyloid deposits and formation of neurofibrillary tangles and plaques. Desorption electrospray ionization mass spectrometry imaging enabled label-free elucidation of the spatial distribution of metabolites and lipids in brain tissue samples without any pretreatment. Ceramide Cer(t18:0/34:0(34OH)), m/z 822.54, and sulfatides, ST18:0, m/z 806.54; ST(d18:1/h22:0), m/z 878.60; ST(24:1), m/z 888.62, and ST(d18:1/h24:0), m/z 906.62 showed upregulation with significant differences in brain tissue from mice exposed to dirty air as compared to filtered air (control). The upregulation of ceramide resulted in formation of neurofibrillary tangles and plaques. Moreover, upregulation of sulfatides might enhance the leakiness of the blood brain barrier by weakening myelin sheaths. Although limited by sample number, our results strongly suggest that prolonged exposure to dirty air contributes to the observed increase in the incidence of cognitive decline and dementia, such as Alzheimer's disease.

Capacitive effect in ultrafast laser-induced emission from low conductance diamond nanotips

Single crystal diamond nanotips reveal a new behavior for ultrafast laser-induced electron emission. Under tightly focused femtosecond laser illumination, electron yield shows a saturation with the laser intensity. When the DC bias is sufficient for dark field emission, large optical intensities can switch off the emission occurring between laser pulses during a few hundred μs, because of the low conductance of the diamond tip. We propose a macroscopic model to combine a capacitive effect with the different conduction and emission mechanisms. This study shows that non-metallic photocathodes offer different perspectives from the conventional metallic ones.

Two-step-model of photosensitivity in cerium-doped fibers

The photosensitivity of various cerium-doped fibers has been experimentally investigated for both excimer- and femtosecond-laser illumination. The results of single-pulse, few-pulse and multi-pulse inscription of fiber-Bragg-gratings with both laser systems and the thermal aging of those gratings demonstrated the restrictions of the conventional color center model for cerium-doped fibers. To explain the short-term stability of single-pulse gratings against long-term stability of multi-pulse gratings, an extension into a two-step-model was deduced.

Characteristic research of uniform-doping and exponential-doping Ga1-xAlxAs/GaAs photocathode with femtosecond laser illumination

The properties and characteristics of graded Al component Ga1-xAlxAs/GaAs photocathode are investigated in this paper, especially the transient reflectivity of Ga0.37Al0.63As under the condition of femtosecond laser illumination. Using software CASTEP, we calculate and analyze the optoelectronic property of varied Al composition Ga1-xAlxAs photocathode based on first principle theory. Ga0.37Al0.63As is emphasized studied because its lattice constant is very close to GaAs, reducing the probability of lattice mismatch and the back interface recombination velocity on the interface of substrate and emission layer. In this work, we design two reflection mode GaAs photocathode samples with different doping method: uniform-doping and exponential-doping used in emission layer grown by MBE. The impacts of different doping method on photocathode are analyzed by comparing some typical performance parameters. Transient reflectivity rates of different doping method Ga1-xAlxAs/GaAs photocathode are investigated by the device of pump-probe transient reflectivity system in the paper and we found that the way of exponential-doping is better for improving the performance of Ga1-xAlxAs /GaAs photocathode. The potential value of transient property of photocathode is enormous in future.

Children's Urinary Environmental Carbon Load. A Novel Marker Reflecting Residential Ambient Air Pollution Exposure?

Ambient air pollution, including black carbon, entails a serious public health risk because of its carcinogenic potential and as climate pollutant. To date, an internal exposure marker for black carbon particles that have cleared from the systemic circulation into the urine does not exist. To develop and validate a novel method to measure black carbon particles in a label-free way in urine. We detected urinary carbon load in 289 children (aged 9-12 yr) using white-light generation under femtosecond pulsed laser illumination. Children's residential black carbon concentrations were estimated based on a high-resolution spatial temporal interpolation method. We were able to detect urinary black carbon in all children, with an overall average (SD) of 98.2 × 105 (29.8 × 105) particles/ml. The urinary black carbon load was positively associated with medium-term to chronic (1 mo or more) residential black carbon exposure: +5.33 × 105 particles/ml higher carbon load (95% confidence interval, 1.56 × 105 to 9.10 × 105 particles/ml) for an interquartile range increment in annual residential black carbon exposure. Consistently, children who lived closer to a major road (≤160 m) had higher urinary black carbon load (6.93 × 105 particles/ml; 95% confidence interval, 0.77 × 105 to 13.1 × 105). Urinary black carbon mirrors the accumulation of medium-term to chronic exposure to combustion-related air pollution. This specific biomarker reflects internal systemic black carbon particles cleared from the circulation into the urine, allowing investigators to unravel the complexity of particulate-related health effects.