Proposed Fluorescence Method Research Articles

Green synthesis of gardenia seeds-based carbon dots for bacterial imaging and antioxidant activity in aqueous and oil samples.

In this work, luminescent carbon dots with gardenia seeds as carbon precursors (GCDs) were synthesized using a one-step mild pyrolysis process and were then used as probes for imaging of bacterial (Escherichia coli). The GCDs showed a strong emission at 430 nm when excited at 370 nm. The relative fluorescence quantum yield of GCDs was found to be 1.13% in an aqueous medium. Rapid internalization of the GCDs by bacteria was confirmed by three colors (blue, green, and yellow) images that were obtained using confocal fluorescence microscopy. In addition, GCDs were noted to exhibit potent scavenging activities against DPPH˙, ˙OH, and ˙O2- free radicals. GCDs were also assayed as antioxidants in an oil sample by volumetric determination of the peroxide value. Thus, GCDs exhibited good antioxidant properties both in aqueous and oil media. In addition, a free fatty acid quantification kit in the presence of GCDs showed enhanced fluorescence detection of palmitic acid with a remarkably good limit of detection of 0.08 μM, which is lower than that in the absence of GCDs (0.76 μM). The proposed fluorescence method was then successfully used to determine the concentration of palmitic acid spiked in milk powder samples, with spiked recoveries of 82.6-109.6% and relative standard deviations of 0.9-4.6%.

Reduced graphene oxide quenched peptide probe for caspase-8 activity detection and cellular imaging.

Cysteinyl aspartate-specific protease 8 (caspase-8) plays a key role in various biological processes by regulating apoptosis. Therefore, this makes accurate detection and intracellular imaging of caspase-8 of great importance for drug screening, disease diagnosis, and prognostication. Here, by designing a reduced graphene oxide (rGO) quenched peptide probe, we constructed a new biosensing system for monitoring in vitro and intracellular caspase-8 activity. In this system, a fluorophore-labeled peptide and rGO were used as the substrate of caspase-8 and the fluorophore quencher, respectively. The hydrolysis of caspase-8 on the polypeptide probe substrate can generate two fragments with different lengths. The release of the short fragment labeled with the fluorophore causes recovery of the fluorescence signal (Ex/Em = 520/576nm). Under the optimized conditions, the proposed fluorescence method exhibited a linear response range of 0.2 to 5 U·mL-1 for caspase-8 with a limit of detection (LOD) of 0.2 U·mL-1 in vitro. Furthermore, this method has been successfully applied to monitoring the upregulation of intracellular caspase-8 activity caused by tert-butyl hydroperoxide (TBHP) and fluorouracil. Flow cytometry assay indicated the positive relation between the upregulation of intracellular caspase-8 activity and cell apoptosis rate. In summary, the above results demonstrated the practical application of this method for apoptosis-related cell imaging.

Rapid analysis of quinoxalines in feeds by a fluorescence sensor based on tetraphenylmethane porous organic framework membrane

In this work, a tetraphenylmethane porous organic framework (TPOF) membrane was prepared by mixing fluorescent TPOF into poly (vinylidene fluoride) (PVDF). Combining the advantages of membrane and TPOF, the TPOF membrane exhibited a continuous porous structure, good flexibility, hydrophobic properties and excellent fluorescence performance. Owing to the remarkable selectivity towards quinoxalines, the TPOF membrane was used as a fluorescence sensor for rapid quinoxalines analysis. The mechanism of the TPOF selectivity was studied by density functional theory (DFT) calculation experiments. Compared to other growth promoting drugs, the lowest unoccupied molecular orbital (LUMO) energy state difference between TPOF and quinoxalines was the largest. The linear ranges for the determination of carbadox and olaquindox were 0.3–20.0 and 0.6–20.0 μmol/L with the correlation coefficients (R2) of 0.9904 and 0.9943, respectively. The limit of detection (LOD, S/N = 3) were 96 and 182 nmol/L, respectively. Furthermore, this fluorescence sensor was used for olaquindox determination in feed samples, and the recoveries were varied from 97.4% to 107.7%. The results obtained by the proposed fluorescence method showed a good agreement with that obtained from HPLC method. Overall, this fluorescence sensor has been confirmed excellent performance in the quinoxalines analysis, which reveals extensive application in rapid residual quinoxalines analysis in feed samples.

Polyvinylpyrrolidone-stabilized Pt nanoclusters as robust oxidase mimics for selective detection of ascorbic acid

In this work, the Pt nanoclusters with an average size of 1.7 ± 0.3 nm were prepared by a facile and green method using polyvinylpyrrolidone (PVP) as both stabilizer and reductant. The oxidase-like activity of PVP-stabilized Pt nanoclusters (PVP-Pt NCs) was investigated by the catalytic oxidation of o-phenylenediamine (OPD). The mechanism studies indicated that PVP-Pt NCs performed as oxidase enzyme mimics by catalyzing the dissolved oxygen to generate the reactive oxygen species (singlet oxygen and superoxide anion) intermediates. Ascorbic acid (AA) could also be oxidized to dehydroascorbic acid (DHA) which could react with OPD to generate a fluorescent compound. On the basis of the robust oxidase-like activity of PVP-Pt NCs, both colorimetric assay and fluorescence method for AA determination were established. Compared with colorimetric assay, the fluorescence method showed higher sensitivity and selectivity for AA detection. The proposed fluorescence method with the LOD of 1.17 μM could overcome the interference of most reducing substances and showed promising applications in biosensor. The as-prepared PVP-Pt NCs possessed intrinsic oxidase-like property by catalyzing dissolved oxygen to ROS (superoxide anions (·O 2 - ) and singlet oxygen ( 1 O 2 )) which could oxide the OPD to OPD ox . The inhibition of AA to the catalytic oxidation of OPD was employed to establish the colorimetric assay for AA determination. AA could also be oxidized to DHA by·O 2 - and 1 O 2 intermediates, and the DHA could react with OPD to form QD with a fluorescence emission peak at 434 nm. The fluorescence method for AA detection was carried out when the solution changed to yellow color which was the signal of the reaction terminal. Comparing with colorimetric assay, the fluorescence method exhibited enhanced sensitivity and selectivity.

Quantification of ATP in cell by fluorescence spectroscopy based on generalized ratio quantitative analysis model

In this contribution, fluorescence spectroscopy based on G-quadruplex formation was developed for the quantification of ATP in cell. In the absence of ATP, thioflavin T (ThT) dye can combine with the G-rich ATP aptamer to form an ATP aptamer-ThT G-quandruplex complex, resulting in the enhancement of fluorescence intensity; otherwise, fluorescence intensity of the system will weaken with the addition of ATP, because ATP has a strong affinity with G-rich ATP aptamer and can replace ThT to form an ATP aptamer-ATP complex. A calibration model based on generalized ratio quantitative analysis model was employed to mitigate the influence of scatterers and background absorbers in cell suspensions. The proposed fluorescence method was applied to the quantitative analysis of ATP in two type of cell lines, and achieved satisfactory quantitative results with accuracy comparable to that of the reference method–ATP detection kit. The limit of detection and limit of quantification of the proposed method for ATP in cell were estimated to be 0.22 and 0.66 μM, respectively. This proposed fluorescence method is highly simple and rapid, and does not require the use of fluorescent labeling.

Carbon dots for ratiometric fluorescence detection of morin

The B,N dual-doped carbon dots (B,N-CDs) for ratiometric fluorescence detection the morin were prepared from sodium tetraborate and polyethyleneimine through the single-step hydrothermal method. The B,N-CDs exhibited the optimum excitation and emission wavelength at 340 nm and 467 nm, respectively. Interestingly, the intensities of emission peak at 467 nm of B,N-CDs reduced meanwhile a new peak emerged at 560 nm with the continuous addition of morin, which revealed the ratio fluorescence characteristic between F560nm/F467nm and morin concentration with the linearity range and detection limit of 14.5–32.5 μmol/L and 0.3 μmol/L (S/N = 3), respectively. The interference of common antibiotics and remedies could be ignored when the concentration of morin was detected by the B,N-CDs, which demonstrating the outstanding selectivity. Furthermore, the proposed fluorescence method is used to detect morin in urine with recoveries are 99.8–104.5%. The results of this research indicate the feasibility and practicality of B,N-CDs as an effective fluorescent probe for the determination of morin.

Ultrasensitive, rapid and selective sensing of hazardous fluoride ion in aqueous solution using a zirconium porphyrinic luminescent metal-organic framework

The development of a rapid and sensitive method for the detection of fluoride ion (F−) in aqueous systems is of great significance for human health and environmental monitoring. In this study, a zirconium porphyrinic luminescent metal-organic framework (LMOF), PCN-222, was employed as a novel fluorescent probe for the ultrasensitive, rapid and selective detection of F− in water. The PCN-222 probe was prepared by a facile solvothermal method. It exhibited good fluorescence stability and was highly stable in water. The fluorescence emission of PCN-222 could be effectively and selectively quenched by F− due to the strong coordination affinity of F− to the zirconium clusters in PCN-222. The proposed fluorescence method for F− detection based on PCN-222 probe afforded a linear response range of 1–20 μmol/L and a very low detection limit (0.048–0.065 μmol/L) in reference to many reported F− fluorescent probes. Moreover, a rapid response time (<10 s) was obtained due to the open and uniform pore structure of PCN-222 that allowed the fast diffusion of F− to interact with the zirconium recognition sites. Finally, the PCN-222 probe was successfully applied for the fluorescence detection of F− in real water samples. These results highlight the great application potential of LMOF in the sensing fields.

Facile Fluorescence Dopamine Detection Strategy Based on Acid Phosphatase (ACP) Enzymatic Oxidation Dopamine to Polydopamine.

Facile and effective detection of dopamine (DA) plays a significant role in current clinical applications. Substantially, special optical nanomaterials are important for fabricating easy-to-control, cheap, selective, and portable fluorescence DA sensors with superior performance. Herein, carbon dots (CDs) prepared from melting method were applied as signal to establish a simple but effective fluorescence strategy for DA determination based on the enzymatic activity of acid phosphatase (ACP), which induces DA to form polydopamine (pDA). The formed pDA caused by the enzymatic oxidization of ACP toward DA can interact with CDs through the inner filter effect. Such behavior effectively quenched the CDs' fluorescence. The degree of fluorescence quenching of CDs was positively correlated with the DA content. Under the optimized reaction conditions, the proposed fluorescence method exhibited a comparable analytical performance with other DA sensors with good selectivity. Furthermore, this method has been successfully applied to detect DA in DA hydrochloride injection and human serum samples. It shows that this method features potential practical application value and is expected to be used in clinical research.

Activity assay and intracellular imaging of APE1 assisted with tetrahedral DNA nanostructure modified-dnazyme and molecular beacon

Human apurinic/apyrimidinic endonuclease 1 (APE1) is an emerging target for sensitizing tumor cells to radiation and chemotherapy due to its critical function in DNA repair and reduction-oxidation regulation. Thus, accurate detection and intracellular imaging of APE1 hold great promise for drug screening, cancer diagnosis and prognosis evaluation. Here, a DNAzyme modified tetrahedral DNA nanostructure (DZ-TDN) and molecular beacon (MB) incorporated biosensing system was developed to reliably monitor intracellular APE1 activity. DZ-TDN was self-assembled from four single-stranded DNAs, one of which contained an extrude DNAzyme sequence on the 5′-end. At normal status, DNAzyme activity was plugged by performing a duplex with a blocker strand containing an AP site. The digestion of APE1 on this site can restore DNAzyme activity, which consequently trigger MB cleavage recycle to amplify detection signal. The results indicated that the proposed fluorescence method showed a linear response ranged for APE1 from 0.01 to 1 U mL−1 with a limit of detection (LOD) of 0.01 U mL−1 (S/N = 3). Moreover, the strategy was successfully used for effectors screening and intracellular imaging of APE1 with high reliability.

Hydrothermal synthesis of carbon dots and their application for detection of chlorogenic acid.

A novel and sensitive fluorescence analysis platform was constructed for the detection of chlorogenic acid (CGA) using carbon dots (C-dots) with prominent sensitivity and selectivity. Excitation-dependent emission fluorescence C-dots were fabricated using citric acid and l-histidine as precursors through an efficient one-step hydrothermal treatment. The maximum excitation and emission wavelength of the as-synthesized C-dots were 340 nm and 414 nm, respectively. Moreover, the as-prepared C-dots displayed excellent water solubility and good photostability. The fluorescence quantum yield of the as-prepared C-dots was measured to be about 22% using quinine sulfate as the reference. Furthermore, the obtained C-dots were applied to the detection of CGA accompanied with a wide linear range from 1.53 μmol L-1 to 80.0 μmol L-1 as well as a limit detection of 0.46 μmol L-1 . More importantly, the proposed fluorescence method was successfully used to analyse CGA in coffee and honeysuckle.

An ultra-selective fluorescence method with enhanced sensitivity for the determination of manganese (VII) in food stuffs using carbon quantum dots as nanoprobe

A novel fluorescence method was for the first time established for the efficient determination of permanganate (Mn(VII)) based on sulfur, chlorine and nitrogen co-doped carbon quantum dots (S,Cl,N-CQDs). The S,Cl,N-CQDs was prepared via a fast and simple acid-base neutralization method. The fluorescence of S,Cl,N-CQDs could be dramatically quenched by Mn(VII) ascribed to a combination of inner filter effect (IFE) and dynamic quenching. Under the optimal working conditions, the S,Cl,N-CQDs-based nanoprobe exhibited high selectivity and sensitivity towards Mn(VII) sensing. A good linear Stern-Volmer equation was obtained for Mn(VII) in a wide concentration range of 0.05–110 μM with a detection limit as low as 12.8 nM. The proposed fluorescence method also exhibits additional advantages of great simplicity, fast in analysis and low cost. The as-fabricated fluorescent nanoprobe was successfully applied for the determination of Mn(VII) in vegetable, cereal and tea samples with high accuracy. It is anticipated that the S,Cl,N-CQDs-based nanoprobe could be further exploited to construct a nanoprobe device for Mn(VII) monitoring in complex food matrix.

Fluorescence "on-off-on" Assay of Copper Ions and EDTA Using Amino-Functionalized Graphene Quantum Dots.

Copper is an important trace element involved in several physiological processes. The deficiency or excess of Cu in the human body may cause some serious diseases. EDTA has been widely employed in many industry fields owing to its excellent chelating ability. The poor biodegradability of EDTA makes itself a persistent substance in the natural environment. This work provided a fluorescence "on-off-on" strategy for the sequential determination of trace Cu2+ and EDTA. Amino-functionalized graphene quantum dots (afGQDs) were synthetized via the thermal pyrolysis of citric acid. Fluorescence resonance energy transfer (FRET) between afGQDs and 1-(2-pyridylazo)-2-naphthol (PAN) effectively quenched the fluorescence of this carbon-based nanomaterial. The generation of the Cu2+-PAN complex caused the increased FRET efficiency and the further fluorescence decline. The change of the fluorescence intensity sensitively responded to copper ions. The linear range and the limit of detection (LOD) were 1nM-10μM and 0.87nM, respectively. EDTA could decompose the Cu2+-PAN complex and liberate PAN, which weakened the FRET efficiency and led to the fluorescence recovery. The increasing degree of the fluorescence intensity was closely related to EDTA within a concentration range from 10nM to 10μM with a LOD at 4nM. Copper ions in the water and human serum samples and EDTA in the trypsin-EDTA sample were successfully detected based on the proposed fluorescence method.

A sensitivity enhanced fluorescence method for the detection of ferrocyanide ions in foodstuffs using carbon nanoparticles as sensing agents

A novel fluorescent nanoprobe was for the first time developed for the efficient detection of ferrocyanide ions ([Fe(CN)6]4−) based on nitrogen (N), sulfur (S) and chlorine (Cl) co-doped carbon nanoparticles (N,S,Cl-CNPs). The N,S,Cl-CNPs were fabricated through a simple and ultrafast acid-base neutralization method. The sensing mechanism was based on the quenching effect of [Fe(CN)6]4− on the fluorescence emission of N,S,Cl-CNPs via dynamic interaction. The N,S,Cl-CNPs were found to show high selectivity and sensitivity towards [Fe(CN)6]4− detection with two good linear relationships were achieved in the concentration ranges of 0.01–1.0 μg/mL and 1.0–50.0 μg/mL, respectively, and the detection limits are as low as 3.3 and 21.8 ng/mL, respectively. The proposed fluorescence method was successfully applied for [Fe(CN)6]4− analyses in food samples with high accuracy. The results of this study indicate the great application prospects of N,S,Cl-CNPs for [Fe(CN)6]4− detection in complex food matrix.

Investigation of photo-induced electron transfer between amino-functionalized graphene quantum dots and selenium nanoparticle and it's application for sensitive fluorescent detection of copper ions

Copper ions play an essential role in some biological processes. Currently, there is a need for the development of convenient and reliable analytical methods for the Cu2+ measurement. In the present work, a sensitive fluorescence method was developed for the determination of copper ions. Amino-functionalized graphene quantum dots (af-GQDs) and selenium nanoparticles (Se NPs) were synthetized, respectively, and they were characterized via transmission electron microscope, infrared spectrum analysis and X-ray photoelectron spectrum measurement. Photo-induced electron transfer (PET) between the prepared two nanomaterials could effectively quench the fluorescence of af-GQDs. Cu(II) was reduced to Cu(I) in the presence ascorbic acid and Cu2Se was finally generated on Se NPs surface, which led to the declined PET efficiency and inhibited the fluorescence quenching of af-GQDs. The change in fluorescence intensity was linearly correlated to the logarithm of the Cu2+ concentration from 1 nM to 10 μM, with a detection limit of 0.4 nM under the optimal conditions. The detections of copper ions in water samples were realized via standard addition method and the recovery values varied from 98.7% to 103%. The proposed fluorescence method was also employed to analyze the uptake of Cu2+ into human cervical carcinoma HeLa cells and cisplatin-resistant HeLa cells (HeLa/DDP cells). The experimental results indicate that the decreased hCTR1 expression level in HeLa/DDP cells weakened the uptake of copper ions into these drug-resistant tumor cells.

Nitrogen and chlorine dual-doped carbon nanodots for determination of curcumin in food matrix via inner filter effect

In this work, a novel simple, fast, selective and inexpensive fluorescence method for the determination of curcumin based on the fluorescence quenching of nitrogen and chlorine dual-doped carbon nanodots (N,Cl-CDs) was for the first time presented. The N,Cl-CDs were fastly and greenly produced by simply mixing glucose, 1,2-ethylenediamine (EDA) and hydrochloric acid (HCl). The fluorescence of N,Cl-CDs was significantly quenched by curcumin via a synergistic effect of dynamic quenching and inner filter effect (IFE). The N,Cl-CDs shows high selectivity and sensitivity towards curcumin sensing, achieving a linear range of 0.1–35 μM and a limit of detection (LOD) as low as 38 nM. The proposed fluorescence method was successfully utilized for curcumin detection in food samples with recoveries in a range of 96.8–106.1%. The findings of this study suggest the feasibility and usefulness of N,Cl-CDs as an effective fluorescence probe for the determination of curcumin in complex food matrix.

Core–Shell HA-AuNPs@SiNPs Nanoprobe for Sensitive Fluorescence Hyaluronidase Detection and Cell Imaging

A highly sensitive and selective fluorescence strategy for hyaluronidase assay was developed by coupling silicon nanoparticles (SiNPs) as fluorescence indicators with hyaluronic-acid-functionalized gold nanoparticles (HA-AuNPs) as quenchers. With the formation of a core–shell HA-AuNPs@SiNPs nanoprobe by self-assembly, the fluorescence of SiNPs could be quenched by HA-AuNPs through fluorescence resonance energy transfer (FRET). The addition of hyaluronidase leads to cleavage of HA into small fragments, and SiNPs are released. As a result, an immediately fluorescent recovery appears when HAase is introduced. The proposed fluorescence method showed a linear response ranged for HAase from 0.01 to 10 U/mL, and a detection limit of 0.004 U/mL (S/N = 3) was obtained. Furthermore, it can be employed as an enzyme activatable nanoprobe for cell imaging applied in diagnostic and related biological studies.

Ultrafast and Energy-saving Synthesis of Nitrogen and Chlorine Co-doped Carbon Nanodots via Neutralization Heat for Selective Detection of Cr(VI) in Aqueous Phase.

In this work, it is presented for the first time that nitrogen and chlorine co-doped carbon nanodots (N,Cl-CDs) were synthesized by simply mixing glucose, concentrated hydrochloric acid (HCl), and 1,2-ethylenediamine (EDA). No external heat was employed; the neutralization reaction served as the heat source. The glucose served as the carbon source while EDA and HCl were the N and Cl dopants, respectively. The fluorescence of N,Cl-CDs was adequately quenched by hexavalent chromium Cr(VI) based on a combination of dynamic quenching and inner filter effect (IFE). Accordingly, an efficient N,Cl-CDs-based fluorescence probe was established for sensitive and selective detection of Cr(VI). The proposed fluorescence sensor provides a linear recognition range for Cr(VI) determination from 3 to 40 µM with a limit of detection (LOD) of 0.28 µM (14.6 µg/L). The proposed fluorescence method was successfully utilized to detect Cr(VI) in different water samples with satisfactory results. The spike recoveries vary from 97.01% to 103.89% with relative standard deviations (RSDs) of less than 0.82%. This work highlights the development of a simple, ultrafast, and energy-saving one-step synthetic route to fabricate N,Cl-CDs for highly selective and sensitive detection of Cr(VI) in real water samples. It is anticipated that the proposed fluorescence method could be further explored and widely used for Cr(VI) detection in the environmental industry.

Multiplexed fluorescence detection of microRNAs based on novel distinguishable quantum dot signal probes by cycle amplification strategy

MicroRNA (miRNA) is a biomarker that has great potential for the diagnosis and prediction of different cancers. Exploring a rapid and specific method for detecting miRNA has become a research hotspot. In this study, a novel strategy for simultaneous fluorescence detection of dual target miRNAs (miRNA-141 and miRNA-21) based on two distinguishable CdSe@ZnS and CdTe quantum dot (QD) probes by target recycling amplification strategy was reported. The hairpin (HP) DNA was firstly linked to the magnetic bead@Au (MB@Au) complex, then the present target miRNAs hybridized with HP, which then initiated the exonuclease III-aided target recycling process, leading to the generation of numerous intermediate DNA sequences (s1) on MB@Au. Subsequently, a large number of QDs fluorescence probes were introduced to hybridize with s1, which will further trigger the scission with addition of Nb.BbvCI. Through convenient magnetic separation, much amplified fluorescence signal of QDs was detected, which has a quantitative relation with the target miRNAs. Importantly, two kinds of distinguishable fluorescent QDs probes were applied to the simultaneous detection of dual miRNAs by cycling amplification strategy. Thus, the proposed fluorescence method could be used to rapidly detect miRNA-141 and miRNA-21 with high sensitivity, and effectively distinguished single-base-mismatched miRNA sequences with high specificity. Therefore, this strategy holds great potential for sensitive, efficient and convenient detection of various tumor markers in clinical application.

Spectroscopic study on the reactions of bis-salophen with uranyl and then with fructose 1,6-bisphosphate and the analytical application

The chelating reaction of bis-salophen with uranyl to form binuclear complex uranyl-bis-salophen (UBS) was studied by fluorescence spectroscopy. The coordination reaction of UBS with fructose 1,6-bisphosphate (F-1,6-BP) to form supramolecular polymer was then studied by resonance light scattering (RLS) spectroscopy. The reaction of bis-salophen with uranyl results in a remarkable enhancement of fluorescence intensity. The maximum emission wavelength of the fluorescence is at 471nm. The reaction of UBS with F-1,6-BP results in a remarkable enhancement of RLS intensity. The maximum scattering wavelength of the RLS is at 460nm. The two reactions were used to establish fluorescence method for the determination of uranium (VI) and RLS method for the determination of F-1,6-BP, respectively. Under optimum conditions, the linear ranges for the detection of uranium (VI) and F-1,6-BP are 0.003–0.35nmol/mL and 0.05–5.0nmol/mL, respectively. The detection limits are 0.0017nmol/mL and 0.020nmol/mL, respectively. The proposed fluorescence method has been successfully applied for the determination of uranium (VI) in environmental water samples with the recoveries of 97.0–104.0%. The proposed RLS method has also been successfully applied for the determination of F-1,6-BP in medicine injection samples with the recoveries of 98.5–102.3%.

A simple in vitro fluorescence method for biomass measurements in algal growth inhibition tests

The estimation of biomass concentrations in algal growth inhibition tests from measurements of pigment fluorescence in extracts of 20% sample (final v/v) prepared by direct addition to dimethylsulfoxide/acetone solvent offers several advantages compared to currently used direct or indirect methods. The extraction stops the electron transfer and other processes which interact with chlorophyll fluorescence when measured in vivo. As a result the response is stabilized and the sensitivity improved. The injection method is very fast, has a high potential for automation, allows storage of samples and is suitable for small sample volumes (e.g., 0.2 ml). The typical initial cell density in standard toxicity tests of 10 4 cells ml −1 of Selenastrum capricornutum was measured precisely with a standard fluorimeter set-up, and 10 3 cells ml −1 of S. capricornutum was measured reliably with a sensitive fluorimeter. At low levels of toxicity by the model test compound potassium dichromate, the proposed fluorescence method resulted in very similar inhibition figures as obtained with electronic particle counting. At high levels of toxicity, on the other hand, biomass determinations from pigment fluorescence readings were markedly affected by toxicant-induced changes of the algal physiology. The low effect part of a dose response curve is normally that one of major interest, and biomass estimation errors associated with fluorescence measurements on extracts are thus considered acceptable in most situations. When the entire dataset was applied for endpoint estimation by the Weibull model, EC-1 estimates were markedly affected by the curve fitting to data in the high inhibition range, while EC-10 and EC-20 were less and EC-50 almost unaffected. The method is expected to be less suitable for toxicity testing of herbicides specifically inhibiting photosynthesis.