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Fluorescent particle tracking is a powerful technique for studying intracellular transport and microrheological properties within living cells, which in most cases employs exogenous fluorescent tracer particles delivered into cells or fluorescent staining of cell organelles. Herein, we propose an alternative strategy, which is based on the generation of fluorescent species in situ with ultrashort laser pulses. Using mouse germinal vesicle oocytes as a model object, we demonstrate that femtosecond laser irradiation produces compact dense areas in the intracellular material containing fluorescent carbon dots synthesized from biological molecules. These dots have tunable persistent and excitation-dependent emission, which is highly advantageous for fluorescent imaging. We further show that tight focusing and tuning of irradiation parameters allow precise control of the location and size of fluorescently labeled areas and minimization of damage inflicted to cells. Pieces of the intracellular material down to the submicrometer size can be labeled with laser-produced fluorescent dots in real time and then employed as probes for detecting intracellular motion activity via fluorescent tracking. Analyzing their diffusion in the oocyte cytoplasm, we arrive to realistic characteristics of active forces generated within the cell and frequency-dependent shear modulus of the cytoplasm. We also quantitatively characterize the level of metabolic activity and density of the cytoskeleton meshwork. Our findings establish a new technique for probing intracellular mechanical properties and also promise applications in tracking individual cells in population or studies of spatiotemporal cell organization.

Recipient cytoplast preparation, commonly performed by DNA aspiration with a needle, inevitably leads to the loss of reprogramming factors. As an alternative to the traditional enucleation technique, femtosecond laser enucleation can eliminate DNA effectively without loss of reprogramming factors and without oocyte puncturing. In this work we have performed oocyte enucleation by destructing the metaphase plate using a 795 nm femtosecond laser. The disability of the enucleated oocytes to develop after the parthenogenetic activation, as well as the lack of DNA staining luminescence, strongly confirms the efficiency of the femtosecond laser enucleation. The parthenogenetic development of oocytes after the cytoplasm treatment suggests a low-invasive effect of the laser enucleation technique.

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Owning to excellent optical properties and high bio-compatibility carbon dots (CDs) have drawn increasing attention and have been widely applied as imaging agents for various bio-applications. Here we report a strategy for live-cell fluorescent bioimaging based on in situ synthesis of CDs within cells by tightly focused femtosecond laser pulses. Laser-produced carbon dots exhibit bright excitationdependent fluorescence and are highly two-photon active under near infrared femtosecond excitation, thus demonstrating a potential for two-photon fluorescence imaging. The Raman spectra of fluorescent centers show strong D (1350 cm -1 ) and G (1590 cm -1 ) bands, thus suggesting that they are composed of carbon dots with sp 2 -hybridyzed core. Using Mouse GV oocytes as a model system we examine cytotoxicity and demonstrate the possibility of long-term fluorescent intracellular tracking of the laser-produced CDs. Created virtually in any point of the live cell, CD-based fluorescent µm-sized markers demonstrate high structural stability and retain bright fluorescence many hours after formation. Our results point to laser-produced fluorescent CDs as a highly-potent tool for cell cycle tracking, culture cell marking and probing intracellular movements.