Fluorescence Excitation Spectra Research Articles

Rydberg-State Double-Well Potentials of Van der Waals Molecules

Recent progress in studies of Rydberg double-well electronic energy states of MeNg (Me = 12-group atom, Ng = noble gas atom) van der Waals (vdW) molecules is presented and analysed. The presentation covers approaches in experimental studies as well as ab initio-calculations of potential energy curves (PECs). The analysis is shown in a broader context of Rydberg states of hetero- and homo-diatomic molecules with PECs possessing complex ‘exotic’ structure. Laser induced fluorescence (LIF) excitation spectra and dispersed emission spectra employed in the spectroscopical characterization of Rydberg states are presented on the background of the diverse spectroscopic methods for their investigations such as laser vaporization–optical resonance (LV-OR), pump-and-probe methods, and polarization labelling spectroscopy. Important and current state-of-the-art applications of Rydberg states with irregular potentials in photoassociation (PA), vibrational and rotational cooling, molecular clocks, frequency standards, and molecular wave-packet interferometry are highlighted.

Interferometric excitation fluorescence lifetime imaging microscopy

Fluorescence lifetime imaging microscopy (FLIM) is a well-established technique with numerous imaging applications. Yet, one of the limitations of FLIM is that it only provides information about the emitting state. Here, we present an extension of FLIM by interferometric measurement of fluorescence excitation spectra. Interferometric Excitation Fluorescence Lifetime Imaging Microscopy (ixFLIM) reports on the correlation of the excitation spectra and emission lifetime, providing the correlation between the ground-state absorption and excited-state emission. As such, it extends the applicability of FLIM and removes some of its limitations. We introduce ixFLIM on progressively more complex systems, directly compare it to standard FLIM, and apply it to quantitative resonance energy transfer imaging from a single measurement.

Room temperature luminescence of 1,N2-etheno-2-aminopurine in poly (vinyl alcohol) films.

We studied spectral properties of 1,N2-etheno-2-aminopurine after immobilization in poly (vinyl alcohol) films. The absorption spectrum of 1,N2-ε2APu consists of two peaks centered at 300 and 370 nm, and the fluorescence spectrum has maximum at about 460 nm. The fluorescence quantum efficiency is 62%. The fluorescence anisotropy reaches a value of 0.3 at longer wavelengths, while it is low at shorter wavelengths (corresponding to the second single excited state). The 1,N2-ε2APu has a relatively long fluorescence lifetime of about 16 ns and a noticeable room temperature phosphorescence with a lifetime of about 220 ms. A broad phosphorescence emission band (425-675 nm) is centered at about 530 nm and markedly overlaps with fluorescence at shorter wavelengths. Surprisingly, the phosphorescence excitation spectrum of 1,N2-ε2APu-doped poly (vinyl alcohol) film differs from the absorption and fluorescence excitation spectra. The strongest room temperature phosphorescence excitation is about 335 nm. At longer excitation wavelengths, above 450 nm, where fluorescence cannot be excited, a triplet excitation is still possible. The 1,N2-ε2APu phosphorescence anisotropy spectra confirm direct triplet state excitation. The ability to excite molecules at long wavelengths can find applications in the study of biological molecules that are unstable when excited at high energies.

Broadband rapid-scanning phase-modulated Fourier transform electronic spectroscopy

We present a phase-modulated approach for ultrabroadband Fourier transform electronic spectroscopy. To overcome the bandwidth limitations and spatial chirp introduced by acousto-optic modulators (AOMs), pulses from a 1 µm laser are modulated using AOMs prior to continuum generation. This phase modulation is transferred to the continuum generated in a yttrium aluminum garnet crystal. Separately generated phase-modulated continua in two arms of a Mach-Zehnder interferometer interfere with the difference of their modulation frequencies, enabling physical under-sampling of the signal and the suppression of low-frequency noise. By interferometrically tracking the relative time delay of the continua, we perform continuous, rapid-scanning Fourier transform electronic spectroscopy with a high signal-to-noise ratio and spectral resolution. As proof of principle, we measure the linear absorption and fluorescence excitation spectra of a laser dye and various biological samples.

Impact of the spatial structure of alkyl chains on properties of thiophene-substituted diketopyrrolopyrroles: Part II – Spectroscopic study

The study concerns the impact of a difference in geometry of the side alkyl chains of oligothiophene derivatives of diketopyrrolopyrrole (DPP) on their spectroscopic properties and aggregation in solutions, in Langmuir layers, and thin films. Using a combination of theoretical and experimental approaches, this study aims to explain the aggregating behaviour of thiophene-substituted DPP derivatives. Various methods were used to characterise the dyes, including absorption spectroscopy also with polarized light, fluorescence spectroscopy, Langmuir techniques, and time-dependent density functional theory (TD-DFT) calculations. The presented results emphasise a significant impact of side alkyl chains on DPP's molecular behaviour, notably evident in thin-layer structures. Interestingly, the deconvolution of the absorption spectra revealed three bands in the red region. Insightful analysis of temperature-dependent absorption, excitation, and emission fluorescence spectra indicates the co-existence of monomer, dimer, and a higher aggregate forms, most likely a tetrameric structures. Moreover, such a complexity of molecular organisation of dyes appears already in the solution. Differences in spectral properties of the dyes studied are robustly visible in changes in the spectra of the air–water interface, where the dye with the branched side group changes the mutual orientation in dimeric structures, leading to the formation of H-type aggregates, which was observed as an almost 20-nm spectral blue shift during Langmuir layer compression. The results presented highlight the need for care in interpretation of the intensity ratio of DPP spectra and spectral shift as the sole determinants of the aggregation state.

A facile synthesis of water-soluble copper nanoclusters as label-free fluorescent probes for rapid, selective and sensitive determination of alizarin red

Copper nanoclusters (FA@CuNCs) emitting blue fluorescence were successfully developed via a one-pot technique. In this method, the copper chloride, folic acid and hydrazine hydrate were applied as a precursor, protective agent and reducing agent, respectively. The absorption, fluorescence excitation and emission spectra of FA@CuNCs were carried out by using ultraviolet–visible and fluorescence spectrometry, respectively. The morphology, particle size, functional groups, oxidation states of elements of FA@CuNCs were discussed via using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The stability of FA@CuNCs was studied under various conditions, such as storage time at 25 ℃, ultraviolet radiation time, sodium chloride solutione and pH. The FA@CuNCs displayed blue fluorescence under the excitation wavelength of 361 nm, and the fluorescence quantum yield was 7.45 %. As a result of the inner filter effect, the alizarin red could significantly weaken the blue fluorescence of FA@CuNCs. Thus, the as-prepared FA@CuNCs could be utilized as fluorescence nanosensors for the trace determination of alizarin red. This platform suggested an excellent linear range for alizarin red varying from 0.5 to 200 μM with a fitting coefficient of 0.9955. The detection limit was calculated to be 0.064 μM in the light of the 3b/k (b and k refer to the standard deviation and slope of fitted curve, respectively). Furthermore, the as-developed FA@CuNCs could be used to detect the alizarin red in real samples and for the sensing of temperature.

Fluorescence Excitation and Dispersed Fluorescence Spectra of the First Electronic Excited (S1) State of peri-Hexabenzocoronene (C42H18) Isolated in Solid para-Hydrogen.

Large polycyclic aromatic hydrocarbons (PAH) and their cationic, hydrogenated, and protonated derivatives have long been considered as promising candidates for the carriers of the diffuse interstellar bands. peri-Hexabenzocoronene (peri-HBC, C42H18) is a large, compact PAH, and, to the best of our knowledge, the largest centrosymmetric all-benzenoid PAH for which electronic spectroscopy data has been published. In this work, we present the dispersed fluorescence and fluorescence excitation spectra of the first electronic excited (S1) state of peri-HBC isolated in solid para-H2 and provide the first detailed vibronic analysis of observed features. The observed spectra agree with the emission and absorption spectra simulated according to optimized geometries and scaled harmonic vibrational frequencies calculated at the density functional theory (DFT) level using a Franck-Condon Herzberg-Teller approach; the spectral bands are associated solely with vibrational normal modes of approximate e2g symmetry and their combinations with vibrational modes of approximately a1g symmetry. We clearly observed the position of the S1-S0 electronic transition origin of peri-HBC at 22,088 cm-1 (452.7 nm), which was unreported previously. The matrix shift of ∼110 cm-1 to the red relative to the gas-phase value was estimated by comparison of two reported gas-phase bands with our work. Because of the significant deviation from the reported wavelengths of DIB, the weakness of the S1-S0 electronic transitions, and the lack of reported DIB at <400 nm where the intense S4 ← S0 band of peri-HBC is located, peri-HBC is unlikely to contribute to DIB.

Mechanisms of formation of heteroassociates of ATP with ag+ ions

Emission and excitation spectra of fluorescence (FL) were studied for aqueous solutions of ATP with AgNO3 salt at different concentrations of silver nitride and temperatures. It is shown that with increasing Ag+ content and temperature, a complex nature of FL quenching occurs due to the formation of ATP - Ag+ complexes. This quenching occurs when the position of the emission bands and FL excitation of the ATP fluorophore is preserved, and the quenching corresponds to the Stern-Volmer linear dependence. At the same time, the values of KSV and kq and their dependence on the temperature indicate a static quenching mechanism. The binding parameter n indicates that the metal–ligand complexes have a stoichiometric ratio of 1:1, and KA decreases with increasing temperature. In the heteroassociates, energy is transferred by the FRET mechanism, and binding of components is mainly realized due to electrostatic and van der Waals interaction.

New 3-D Fluorescence Spectral Indices for Multiple Pigment Inversions of Plant Leaves via 3-D Fluorescence Spectra

High-sensitivity fluorescence monitoring has been widely used in agriculture and environmental science. However, the active fluorescence detection information of leaf segments mainly focuses on total chlorophyll, and the fluorescence information of chlorophyll a, chlorophyll b, and some other pigments has not been explored. This only considers the fluorescence spectrum characteristics at a single wavelength or the fluorescence integral from a range of wavelength regions and does not completely consider the linkage relation between the excitation, emission, and interference information. In this paper, the three-dimensional fluorescence spectrum, containing the excitation and emission fluorescence spectra, and the corresponding multiple pigment characteristics from the upgraded LOPEX_ZJU database were collected. The linkages of excitation and emission of the three-dimensional fluorescence spectra of these pigments were analyzed for the newly built multiple pigment 3-D fluorescence spectral indices (3-D FSIs), including those of chlorophyll a, chlorophyll b, carotenoid, anthocyanin, and flavonoid 3-D FSIs. Then, these pigment inversion models were established and validated. The results show that the 3-D FSIs performances for the photosynthetic pigment content inversion (including chlorophyll a and b, and carotenoids) were much better than those for the photo-protective pigments (including anthocyanins and flavonoids) from the 3-D fluorescence spectra of these plant leaves. Here, the 3-D fluorescence normalization index (FNI ((F430,690-F430,763)/(F430,690+F430,763))) for the chlorophyll a inversion model has a high accuracy, the RMSE is 2.96 μg/cm2, and the 3-D fluorescence reciprocal difference index (FRI (F650,704/F650,668) for the chlorophyll b model has an encouraging RMSE (2.01 μg/cm2). The RMSE of the 3-D fluorescence ratio index (FRI (F500,748/F500,717)) for the carotenoid inversion is 3.77 μg/cm2 RMSE. Only FRI (F370,615/F370,438) was selected for the modeling and validating evaluation of the leaf Flas content inversion, but the evaluation metrics were not good, with an RMSE (151.13 μg/cm2). For Ants, although there was a 3-D FSI (FRDI (1/F540,679-1/F540,557)), and its evaluation metrics, with an RMSE (2.8 μg/cm2), were at or over 0.05 level, the validating evaluation metric VC (98.3577%) was not encouraging. These results showed that fluorescence, as a nondestructive and efficient detection method, could determine the contents of chlorophyll a, chlorophyll b, and carotenoid in plant leaves, providing a new method to detect plant information. It can also provide a potential chance for the fluorescence images of fine photo-protective pigments, especially chlorophyll a and b, using the special active fluorescence excitation light source and a few fluorescence imaging channels from the optimal FSIs.

References for Small Fluorescence Quantum Yields.

Three compounds with fluorescence quantum yields in the range of 10- 5 to 10- 4 and emission spectra covering the UV/Vis spectral range are suggested as new references for the determination of small fluorescence quantum yields. The compounds are thymidine (dT) in water, dibenzoylmethane (DBM) in ethanol, and malachite green chloride (MG) in water, representing the blue, green, and red regions of the spectrum, respectively. All compounds are easily handled, photostable, and commercially available. Furthermore, these compounds exhibit a mirror-image symmetry between their absorption and fluorescence spectra. This symmetry, along with closely aligned fluorescence excitation and absorption spectra, confirms that the observed emissions originate from the compounds themselves. The fluorescence quantum yields were determined via a relative approach as well as Strickler-Berg analysis in conjunction with time resolved fluorescence spectroscopy. Within the respective error margins, the two approaches yielded identical results.

Fano resonance in excitation spectroscopy and cooling of an optically trapped single atom

Electromagnetically induced transparency (EIT) can be used to cool an atom in a harmonic potential close to the ground state by addressing several vibrational modes simultaneously. Previous experimental efforts focus on trapped ions and neutral atoms in a standing wave trap. In this work, we demonstrate EIT cooling of an optically trapped single neutral atom, where the trap frequencies are an order of magnitude smaller than in an ion trap and a standing wave trap. We resolve the Fano resonance feature in fluorescence excitation spectra and the corresponding cooling profile in temperature measurements. A final temperature of around 6 µK is achieved with EIT cooling, a factor of 2 lower than the previous value obtained using polarization gradient cooling. Published by the American Physical Society 2024

PHire: A Novel Red Intracellular pH Sensor

Maintaining pH is critical for proper cellular and organ function. To measure intracellular pH, we made a novel genetically encoded protein, pHire, that increases red fluorescence with increasing pH. Thus, pHire allows for the coupling of multiple fluorescent tags without spectral overlap. We have expressed pHire in mammalian epithelial cells, Drosophila, and mice. In this study, our goal was to characterize pHire’s spectral properties by expression in human cells (HEK293) and in E.coli. To biophysically characterize pHire, we made a maltose binding protein (MBP)-pHire fusion protein to purify from E.coli. Pelleting individual colony growths revealed pink bacterial pellets which fluoresced with mCherry filters. Rather than purifying the MBP-pHire protein, equal volumes of bacteria were permeabilized with nigericin and high K+ solution for pH 5 to 9. These aliquots were then used to gather the fluorescence excitation and emission spectra of pHire, allowing us to determine the excitation and emission peaks of pHire as a function of pH. Our results showed peaks at Ex579 nm and Em611 nm, or roughly mCherry. Pelleted bacteria could also be fixed in perfusion chambers, revealing the same calibration curve as in mammalian cells and flies. Next, stable HEK293-pHire cells were selected to assay acid-base transport using NH4Cl or CO2/HCO3− in perfusion experiments. These HEK-pHire cells have less fluorescence than MBP-pHire bacteria but show the same Ex/Em peaks. However, an in-frame ATG 5’ to pHire in a mouse (adding 23 amino acids), removed pHire pH-dependence and decreased bacterial fluorescent output. Together these results indicate that pHire is biophysically similar in cells tested but that unstructured N-terminal additions block pH-responses. Funding: R25-DK101405, R21-DK129897. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A novel near-infrared fluorescent probe for real-time monitoring of leucine aminopeptidase activity and metastatic tumor progression

This article discusses the importance of early tumor detection, particularly in liver cancer, and the role of leucine aminopeptidase (LAP) as a potential marker for liver cancer diagnosis and prognosis assessment. The article highlights the limitations of current tumor markers and the need for new markers and multi-marker approaches to improve accuracy. The authors introduce a novel near-infrared fluorescent probe, NTAP, designed for LAP detection. They describe the synthesis of the probe and evaluate its spectral properties, including the LOD was 0.0038 U/mL, and QY was 0.32 %. The kinetic properties of NTAP, such as the relationship between LAP concentration (0–0.08 U/mL), reaction time (3 min), and fluorescence excitation spectra (475 nm) and emission spectra (715 nm) are investigated. The article also discusses the stability and selectivity of the probe and its ability to detect LAP in complex samples. Cellular imaging experiments demonstrate the NATP specificity and selectivity in detecting LAP activity and its inhibition. Animal models of liver and lung metastasis are used to evaluate the probe's imaging capabilities, showing its ability to accurately locate and detect metastatic lesions. The article concludes by emphasizing the potential applications of the NTAP probe in early tumor diagnosis, treatment monitoring, and the study of tumor metastasis mechanisms.

A dual-signal ECL-RET immunosensor based on VC-g-C3N4 and Ru-Zr-MOF for the detection of β2-MG

This work proposes a novel dual-signal electrochemiluminescence (ECL) immunosensor based on energy resonance transfer (RET) for the detection of β2-Microglobulin (β2-MG). Introducing carbon vacancy into g-C3N4 (VC-g-C3N4) can lead to the narrowing of the band gap and the reduction of LUMO, thereby significantly enhancing the ECL efficiency of the material. Meanwhile, Zr-MOF can effectively load Ru(bpy)32+ (Ru-Zr-MOF), enabling its stable existence on the electrode. The ECL emission spectrum of VC-g-C3N4 overlaps well with the fluorescence excitation spectrum of Ru-Zr-MOF, indicating an effective ECL-RET effect between them. As the concentration of β2-MG increases, the intensity of anodic ECL signal gradually increases, while the intensity of cathodic ECL signal gradually decreases. The difference between the cathodic and anodic ECL signals has a good linear relationship within the concentration range from 0.2 pg/mL to 200 ng/mL, with a detection limit of 27.73 fg/mL. The constructed immunosensor can be used for practical analysis in human serum. The proposed sensor has great potential in clinical detection of β2-MG, providing new insights for biomolecular detection and disease diagnosis.

High-speed fluorescence excitation-scanning hyperspectral imaging microscopy using thin-film tunable filters.

Hyperspectral imaging (HSI) technologies have enabled a range of experimental techniques and studies in the fluorescence microscopy field. Unfortunately, a drawback of many HSI microscope platforms is increased acquisition time required to collect images across many spectral bands, as well as signal loss due to the need to filter or disperse emitted fluorescence into many discrete bands. We have previously demonstrated that an alternative approach of scanning the fluorescence excitation spectrum can greatly improve system efficiency by decreasing light losses associated with emission filtering. Our initial system was configured using an array of thin-film tunable filters (TFTFs, VersaChrome, Semrock) mounted in a tiltable filter wheel (VF-5, Sutter) that required ~150-200 ms to switch between wavelengths. Here, we present a new configuration for high-speed switching of TFTFs to allow rapid time-lapse HSI microscopy. A TFTF array was mounted in a custom holder that was attached to a piezoelectric rotation mount (ThorLabs), allowing high-speed rotation. Switching between adjacent filters was achieved using the internal optics of a DG-4 lightsource (Sutter Instrument), including a pair of off-axis parabolic mirrors and galvanometers. Output light was coupled to a liquid lightguide and into an inverted widefield fluorescence microscope (TI-2, Nikon Instruments). Initial tests indicate that the HSI system provides a 15-20 nm bandwidth tunable excitation band and ~10-20 ms wavelength switch time, allowing for high-speed HSI imaging of dynamic cellular events. This work was supported by NIH P01HL066299, R01HL169522, NIH TL1TR003106, and NSF MRI1725937.

Access to the Antenna System of Photosystem I via Single-Molecule Excitation-Emission Spectroscopy.

In the development of single-molecule spectroscopy, the simultaneous detection of the excitation and emission spectra has been limited. The fluorescence excitation spectrum based on background-free signals is compatible with the fluorescence-emission-based detection of single molecules and can provide insight into the variations in the input energy of the different terminal emitters. Here, we implement single-molecule excitation-emission spectroscopy (SMEES) for photosystem I (PSI) via a cryogenic optical microscope. To this end, we extended our line-focus-based excitation-spectral microscope system to the cryogenic temperature-compatible version. PSI is one of the two photosystems embedded in the thylakoid membrane in oxygen-free photosynthetic organisms. PSI plays an essential role in electron transfer in the photosynthesis reaction. PSIs of many organisms contain a few red-shifted chlorophylls (Chls) with much lower excitation energies than ordinary antenna Chls. The fluorescence emission spectrum originates primarily from the red-shifted Chls, whereas the excitation spectrum is sensitive to the antenna Chls that are upstream of red-shifted Chls. Using SMEES, we obtained the inclining two-dimensional excitation-emission matrix (2D-EEM) of PSI particles isolated from a cyanobacterium, Thermosynechococcus vestitus (equivalent to elongatus), at about 80 K. Interestingly, by decomposing the inclining 2D-EEMs within time course observation, we found prominent variations in the excitation spectra of the red-shifted Chl pools with different emission wavelengths, strongly indicating the variable excitation energy transfer (EET) pathway from the antenna to the terminal emitting pools. SMEES helps us to directly gain information about the antenna system, which is fundamental to depicting the EET within pigment-protein complexes.

Photophysical properties of DAPI in PVA films. Possibility of room temperature phosphorescence

We studied the spectral properties of 4′-6-diamidino-2-phenylindole (DAPI) in poly (vinyl alcohol) (PVA) films. Absorption and fluorescence spectra, emission and excitation spectra, quantum yield, and fluorescence lifetime have been characterized. An efficient room temperature phosphorescence (RTP) of DAPI has been observed with UV and blue light excitations. A few hundred millisecond phosphorescence lifetime enables a gated detection with sufficient background reduction. We found the phosphorescent Quantum Yield of DAPI in PVA Film to be 0.0009.

Registration of Phytoplankton Fluorescence Using an Experimental Sounding Probe

The main optical characteristics of phytoplankton and colored dissolved organic matter are described. The necessity of simultaneous registration of fluorescence of phytoplankton pigments and colored dissolved organic matter in seawater in situ is substantiated. Commercial recording devices, realizing registration of signals of phytoplankton fluorescence intensity in situ, are considered. This paper presents the developed experimental probing autonomous multichannel multichannel meter of fluorescence and light scattering in seawater (FR1). The paper presents the functional scheme of the developed meter, describes its main assemblies and principles of its operation. The developed meter allows quasi-simultaneous registration of a large set of parameters: excitation spectra of phytoplankton fluorescence, fluorescence intensity of phytoplankton pigments (chlorophyll-a, phycoerythrin, phycocyanin, β-carotene), as well as fluorescence intensity of colored dissolved organic matter and spectra of light scattering index at an angle of 90°. Registration of all these parameters is carried out from one measuring volume, where the same composition of suspended matter is located in the process of probing at each specific moment of time. The paper presents the results of approbation of the developed meter and suggests the direction of further research using it.

Unique structural effect on the fluorosolvatochromism and dual fluorescence emission of D-π-A+ cationic chromophores with furyl bridge. An approach to white light emitters

Photophysical behavior of two D − π − A+ cationic compounds with the same furyl bridge and nicotinamidine group as an electron acceptor moiety and two electron donating groups, namely methoxy (I) and N,N-dimethylamino (II) groups was examined using steady-state and time-resolved techniques in variety of solvents. Time-dependent density functional theory (TDDFT) calculations were performed in some representative solvents and compared with the experimental results. Steady state and time-resolved studies in different solvents reveal that fluorescence emission of (I) is ascribed to an emission from an excited state (ICT) with higher dipole moment than the ground state while the emission of (II) is a dual emission from a state with high charge transfer nature (ICT) in addition to the locally excited state (LE). The fluorescence emission spectra of (II) were found to depend on the excitation wavelength and an increase in the excitation wavelength led to the formation of a longer wavelength emission band with lower quantum yield. It has also been found that the fluorescence excitation spectra were dependent on the emission wavelength. The effect of solvent on the nature of dual emission was examined. Correlation of the photophysical properties of the excited states of (I) and (II) with the solvent polarity, ε, reveals the charge transfer nature of (I) and the long wavelength emission band of (II), while their correlation with the solvent polarity parameter (ETN) shows two different trends when the solvents are divided to aprotic and protic solvents. For precise investigation of the impact of each solvent parameter on each photophysical property, Catalán’s and Laurence’s four parametric linear solvation energy relationships were studied. We have found that the non-specific interactions of the solvent are primarily responsible for controlling the photophysical properties, as demonstrated by Catalán's and Laurence's treatments. DFT and TDDFT calculations were used to anticipate the dipole moments in the ground and excited states and geometry of both states.

A Review of in vivo Toxicity of Quantum Dots in Animal Models.

Tremendous research efforts have been devoted to nanoparticles for applications in optoelectronics and biomedicine. Over the past decade, quantum dots (QDs) have become one of the fastest growing areas of research in nanotechnology because of outstanding photophysical properties, including narrow and symmetrical emission spectrum, broad fluorescence excitation spectrum, the tenability of the emission wavelength with the particle size and composition, anti-photobleaching ability and stable fluorescence. These characteristics are suitable for optical imaging, drug delivery and other biomedical applications. Research on QDs toxicology has demonstrated QDs affect or damage the biological system to some extent, and this situation is generally caused by the metal ions and some special properties in QDs, which hinders the further application of QDs in the biomedical field. The toxicological mechanism mainly stems from the release of heavy metal ions and generation of reactive oxygen species (ROS). At the same time, the contact reaction with QDs also cause disorders in organelles and changes in gene expression profiles. In this review, we try to present an overview of the toxicity and related toxicity mechanisms of QDs in different target organs. It is believed that the evaluation of toxicity and the synthesis of environmentally friendly QDs are the primary issues to be addressed for future widespread applications. However, considering the many different types and potential modifications, this review on the potential toxicity of QDs is still not clearly elucidated, and further research is needed on this meaningful topic.