Standard Serum Samples Research Articles

Influence of sample collection tube method, anticoagulant-containing plasma versus serum, on influenza virus hemagglutination inhibition titer and microneutralization titer serological assays

BackgroundThe hemagglutination-inhibition (HAI) assay is a critical component for measurement of immunogenicity in influenza vaccine development. It is unknown if the results can be influenced by sample type and anticoagulants. The purpose of this study was to evaluate the influence of different sample collection methods, in particular different anticoagulants, and choice of plasma or serum, on influenza virus serological assays.MethodsBlood samples from thirty donors previously immunized against influenza viruses were collected using six different types of blood collection tubes, two of which collect serum and four of which contain various anticoagulants for collecting plasma. Serum: (1) serum separator tubes (SST); and (2) Plus Plastic serum “red-top serum” tubes. Plasma: (3) spray-coated K2 ethylenediaminetetraacetic acid (EDTA) tubes: (4) Sodium Heparin tubes; (5) Citrate tubes with 3.2% sodium citrate solution; and (6) Glass Blood Collection tubes with acid citrate dextrose. Samples were tested against three different influenza viruses (A/California/07/2009 (H1N1pdm09), A/Texas/50/2012 (H3N2), and B/Massachusetts/2/2012) for hemagglutination inhibition titer and virus neutralization titer via a microneutralization (MN) assay, and data compared to that obtained for standard serum sample collected in SST.ResultsHAI and MN titers against type A viruses were within two dilutions compared to SST collection method over 96% of the time irrespective of sample type or anticoagulant. However, HAI titers for type B virus were more variable across different collection methods. EDTA plasma samples were greater than two dilutions higher than SST serum samples 70% (21 of 30 samples) of the time. In contrast, MN titers were within two dilutions over 96% of the time, with the highest deviation noted in acid citrate dextrose plasma samples (3 of 30 samples tested, 10%).ConclusionsThese data provide useful guidelines for sample collection and serology testing when screening: (i) influenza vaccine immunogenicity antibody response; (ii) antibody responses to newly emerging viral strains; and (iii) clinical samples for anti-influenza antibody activity.

Electrochemiluminescence Assays for Human Islet Autoantibodies.

Pinpointing islet autoantibodies associated with type 1 diabetes (T1D) leads the way to project and deter this disease in the general population. A novel ECL assay is a nonradioactive fluid phase assay for islet autoantibodies with higher sensitivity and specificity than the current 'gold' standard radio-binding assay (RBA). ECL assays can more precisely define the onset of presymptomatic T1D by distinguishing the high-risk, high-affinity autoantibodies from the low-risk, low-affinity autoantibodies generated in RBAs, and conventional enzyme-linked immunosorbent assays (ELISA). The antigen protein used in this ECL assay is labeled with Sulfo-tag and Biotin, respectively. Each ECL autoantibody assay that uses a particular antigen protein needs an optimization step before it can be used for laboratory application. This step is especially vital in determining the requirements for serum acid treatments, concentrations, and ratios of the two different antigens labeled with Sulfo-tag and Biotin. To perform the assay, serum samples are mixed with Sulfo-tag-conjugated and biotinylated capture antigen protein in phosphate buffered solution (PBS), containing 5% Bovine Serum Albumin (BSA). Afterwards, the samples are incubated overnight at 4 °C. The same day, a streptavidin-coated plate is prepared with blocker buffer and incubated overnight at 4 °C. On the second day, wash the streptavidin plate and transfer the serum-antigen mixture onto the plate. Place the plate on the plate shaker, set it at low speed, and incubate at room temperature for 1 h. Subsequently, the plate is washed again, and reader buffer is added. The plate is then counted on the plate reader machine. The results are conveyed through an index, which is generated from internal standard positive and negative control serum samples.

Electrochemiluminescence Assays for Human Islet Autoantibodies

Pinpointing islet autoantibodies associated with type 1 diabetes (T1D) leads the way to project and deter this disease in the general population. A novel ECL assay is a nonradioactive fluid phase assay for islet autoantibodies with higher sensitivity and specificity than the current 'gold' standard radio-binding assay (RBA). ECL assays can more precisely define the onset of presymptomatic T1D by distinguishing the high-risk, high-affinity autoantibodies from the low-risk, low-affinity autoantibodies generated in RBAs, and conventional enzyme-linked immunosorbent assays (ELISA). The antigen protein used in this ECL assay is labeled with Sulfo-tag and Biotin, respectively. Each ECL autoantibody assay that uses a particular antigen protein needs an optimization step before it can be used for laboratory application. This step is especially vital in determining the requirements for serum acid treatments, concentrations, and ratios of the two different antigens labeled with Sulfo-tag and Biotin. To perform the assay, serum samples are mixed with Sulfo-tag-conjugated and biotinylated capture antigen protein in phosphate buffered solution (PBS), containing 5% Bovine Serum Albumin (BSA). Afterwards, the samples are incubated overnight at 4 °C. The same day, a streptavidin-coated plate is prepared with blocker buffer and incubated overnight at 4 °C. On the second day, wash the streptavidin plate and transfer the serum-antigen mixture onto the plate. Place the plate on the plate shaker, set it at low speed, and incubate at room temperature for 1 h. Subsequently, the plate is washed again, and reader buffer is added. The plate is then counted on the plate reader machine. The results are conveyed through an index, which is generated from internal standard positive and negative control serum samples.

Assay of serum cholinesterase activity by an amperometric biosensor based on a co-crosslinked choline oxidase/overoxidized polypyrrole bilayer.

Based on choline oxidase immobilized by co-crosslinking on an overoxidised polypyrrole modified platinum electrode, a novel electrochemical assay for cholinesterase activity in human serum was developed. The assay was performed by adding an aliquot of cholinesterase standard solution or serum sample to phosphate buffer containing choline or thiocholine ester and measuring the oxidation current of hydrogen peroxide at the rotating modified electrode polarized at +0.7 V vs. SCE. The influence of some experimental parameters such as pH of the assay, mass transport at the electrode, type and concentration of the cholinesterase substrate was studied and optimised. Reversible inhibition of choline oxidase from cholinesterase substrates was evidenced for the first time, which increases in the order of acetylcholine, butyrylcholine and s-butyrylthiocholine. Wide linear range, fast response time and appreciable long-term stability were assured for both acethyl- and butyrylcholinesterase assays. On allowing the polypyrrole layer to efficiently remove interferences from the electroactive compounds in the sample, the present method revealed to be suitable for the detection of butyrylcholinesterase in human serum at activities as low as 0.5 U L-1. The validation with a reference spectrophotometric method showed no significant differences when human serum samples were analysed.

Validation of a flame photometric method for serum lithium estimation

Background Lithium is a first line drug used to treat bipolar affective disorder requiring frequent monitoring due to its narrow therapeutic index. Flame photometry is a reliable quick and cost-effective method of serum lithium estimation. Objective We aimed to validate a flame photometry method for serum lithium estimation to compare the results with a different model flame photometer and an ion-selective electrode. Method Sherwood 410 flame photometer was used for the analysis. Serum samples were diluted 1:2 using a lithium blank solution containing sodium and potassium. Aqueous lithium standards were prepared using the same blank. The method was validated for the concentration range 0.2-1.5mmol/l. Linearity, recovery, accuracy, precision and stability were determined by standard lithium serum samples representing the lower limit of quantification (LLOQ) 0.2mmol/l, median level of quantification (MLOQ) 0.8mmol/l and the upper limit of quantification (ULOQ) 1.5mmol/l. Five replicates of serum and aqueous lithium samples were used to determine linearity in the range between LLOQ and ULOQ using the coefficient of determination (R2). Five standard serum replicates were used for recovery, accuracy and precision studies. Precision was determined by the coefficient of variation (CV%) on three different days. Results of the flame photometric method were compared with those of a different flame photometric method and an ion-selective electrode method. Results: The R2 for the aqueous samples and the serum samples was >0.995 demonstrating linearity. The matrix effect ranged between 92.5% and 105% for the LLOQ, MLOQ and ULOQ. The accuracy and precision for LLOQ, MLOQ of and ULOQ were below 15%. Similar results were obtained for the QC samples with the different model flame photometer and ion-selective electrode method. Conclusion The flame photometric method used in our laboratory is suitable and reliable for determining serum lithium concentrations for use in therapeutic drug monitoring.

The Development of Reproducible and Selective Uric Acid Biosensor by Using Electrodeposited Polytyramine as Matrix Polymer

A versatile method for the construction of reproducible and high selective uric acid biosensor is explained. Electrodeposited polytyramine is used as biosensor matrixes due to its compatibility to immobilize enzyme uric oxidase in the membrane electrode. The precise control over the charge passed during deposition of polytyramine allows concomitant control over the thickness of the deposited enzyme layers onto the surface of the electrode. The uric acid biosensor showed a sensitive response to uric acid with a linear calibration curve lies in the concentration range of 0.1–2.5 mM, slope 0.066 µA mM-1, and the limit detection was 0.01 mM uric acid (S/N = 3). The biosensor shown excellent reproducibility, the variation between response curves for uric acid lies between RSD 1% at low concentrations and up to RSD 6% at saturation concentration. Uric acid biosensor is free from normal interference. The biosensor showed good stability and to be applicable to determine uric acid in real samples. Analysis of uric acid in the reference standard serum samples by the biosensor method are all agreed with the real value from supplier. Standard samples were also analyzed independently by two methods: the present biosensor method and the standard UV-Vis spectrophotometry method, gave a correlation coefficient of 0.994. This result confirms that the biosensor method meets the rigid demands expected for uric acid in real samples.

A novel peptide/Fe3O4@SiO2-Au nanocomposite-based fluorescence biosensor for the highly selective and sensitive detection of prostate-specific antigen

Highly selective and sensitive detection methods are very important for the early diagnosis of prostate-specific antigen (PSA). Here, we present a novel peptide/Fe3O4@SiO2-Au nanocomposite-based fluorescence biosensor for highly selective and sensitive detection of PSA. The biosensor was made by self-organizing 5-FAM labeled peptides onto the surface of magnetic Fe3O4@SiO2-Au nanocomposites (MNCPs), resulting in efficient quenching of the FAM fluorescence. The PSA specifically recognized and cleaved the 5-FAM-labeled peptides, leading to the fluorescence recovery. This is the first report of the MNCPs by in situ growth of Au nanoparticles (AuNPs) on the SiO2 encapsulated single Fe3O4 nanocubes. The MNCPs feature robust salt stability, and allow for effective fluorescence quenching and easy magnetic separation, which greatly decrease the background fluorescence. The peptide/MNCPs-based fluorescence biosensor measure a wide range of concentrations of PSA, from 1.0 × 10−12 to 1.0 × 10−9g/mL, with a limit of detection (LOD) of 3.0 × 10−13g/mL in both standard solutions and serum samples, demonstrating the great potential of this biosensor platform for use in clinical and biological assays.

Determination of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls in human serum using programmable-temperature vaporization gas chromatography with high-resolution mass spectrometry.

The determination of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls in blood from a non-occupational population is essential for the investigation of adverse health effects from these pollutants. In this study, a sensitive method based on programmable-temperature vaporization with large-volume injection coupled with gas chromatography with high-resolution mass spectrometry was developed to determine these pollutants in 1-2mL of human serum samples. Various key parameters of programmable-temperature vaporization injector, including vent temperature, vent time, vent flow, transfer temperature and transfer time were optimized by factorial design. The accuracy and precision as well as applicability were assessed by determining polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls in calibration standard solutions, standard reference materials and real human serum samples from non-occupational population. The method detection limits of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls were 1.5-9.0 and 0.005-0.02ng/kg wet weight, respectively. By comparing with typically splitless injection, the application of programmable-temperature vaporization injector could effectively lead to higher detectable rate of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls in 1-2mL of human serum samples.

Automated Quantitative Enzyme Biosensing in 24-Well Microplates.

We report a novel system for glucose estimation in model and real samples, utilizing enzyme-modified pencil leads (PL) as effective electrochemical biosensors for robotic substrate quantification in 24-well microplates. Electrochemically formed carboxyl groups on the surface of the graphite were cross-linked to amino groups in the enzyme so as to attach glucose oxidase to the PL surface. Automated amperometric sensing of glucose solutions in microtiter-plate wells used computer-controlled stepper motors to move the biosensor/counter/reference electrode assemblies sequentially between the samples. This setup achieved stable analyte response and, in calibration trials, a linear response range and detection limit of 0.1-8 mM and 0.05 ± 0.01 mM, respectively. The biosensor microplate assay offered accurate "hands-off" evaluation of 4 or 20 samples per plate run, in the standard addition or calibration curve mode, respectively. Mode-independent glucose assays in standard solutions and human serum samples worked reproducibly with close to 100% recovery. The choice of cheap and practical PL enzyme biosensors and simple nonmicrofluidic measurement automation offers a convenient, labor- and cost-efficient form of quantitative biosensing, with a reduced risk of operator errors. The robotic approach is best suited to repetitive measurements of sample series, with academic research and clinical, environmental, pharmaceutical, or biotechnological analysis being potential areas for future exploitations of the methodology.

Capacitive DNA sensor for rapid and sensitive detection of whole genome human herpesvirus-1 dsDNA in serum.

This work presents a rapid, highly sensitive, low-cost, and specific capacitive DNA sensor for detection of whole genome human herpesvirus-1 DNA. This sensor is capable of direct DNA detection with a response time of 30s, and it can be used to test standard buffer or serum samples. The sensing approach for DNA detection is based on alternating current (AC) electrokinetics. By applying an inhomogeneous AC electric field on sensor electrodes, positive dielectrophoresis is induced to accelerate DNA hybridization. The same applied AC signal also directly measures the hybridization of target with the probe on the sensor surface. Experiments are conducted to optimize the AC signal, as well as the buffers for probe immobilization and target DNA hybridization. The assay is highly sensitive and specific, with no response to human herpesvirus-2 DNA at 5ng/mL and a LOD of 1.0pg/mL (6.5 copies/μL or 10.7aM) in standard buffer. When testing the double stranded (ds) DNA spiked in human serum samples, the sensor yields a LOD of 20.0pg/mL (129.5 copies/μL or 0.21 femtomolar (fM)) in neat serum. In this work, the target is whole genome dsDNA, consequently the test can be performed without the use of enzyme or amplification, which considerably simplifies the sensor operation and is highly suitable for point of care disease diagnosis.

Perbandingan Penggunaan Konjugat Antibovine IgG-HRP Dan Protein A/G-HRP Dengan Beberapa Larutan Pengencer Serum Pada ELISA Untuk Deteksi Surra Pada Sapi Dan Kerbau

ABSTRACT Surra was reported in various types of animals both livestock, pets and wildlife. ELISA (enzyme linked immunosorbent assay) is a sensitive and specific diagnosis technique for Surra detection. The use of species specific conjugate (anti bovine IgG-HRP) has limited while protein A/G can be used for a wide variety of animal species. This study aimed to evaluate the initial application of the protein A/G-HRP compared with anti bovine IgG-HRP using standard samples using four (4) types of diluent buffer. The standard serum samples (23 serum) consist of positive and negative sera from bovine (cattle and buffalo) were reacted with Surra antigen on microplate. Positive and negative serum was diluted with different diluent buffer, namely PBS-Tween20 (PBST), RBA (RedBuff A), RBB (RedBuff B) and LC (Low Cross). Results of ELISA using protein A/G-HRP showed absorbance values reduced 36.16% - 69.30% compared to the anti-bovine IgG-HRP. The percentage reduction of PBST, RBA, RBB and LC, were 51.76%; 56.64%; 36.16% and 69.30% respectively. The use of protein A/G-HRP and fourth diluent buffer can reduce antigen - antibody bonding with a weak affinity which lowers the absorbance value of ELISA Surra. Keywords : Protein A, Protein G, Surra, ELISA, Trypanosoma evansi

N-Glycosylation analysis of formalin fixed paraffin embedded samples by capillary electrophoresis.

In this study, N-linked glycans from intact, formalin treated and formalin fixed paraffin embedded (FFPE) standard glycoproteins, human serum and mouse tumor tissue samples were investigated in respect to their susceptibility for formaldehyde treatment mediated changes. FFPE samples were first deparaffinized, followed by solubilization in radioimmunoprecipitation assay buffer and treated with PNGase F for N-glycan release. The released glycans were labeled with a charged fluorophore and analyzed by capillary electrophoresis with laser induced fluorescent detection. No significant alterations were found in the N-glycome profile at any of the investigated complexation levels (i.e., glycoprotein, serum and tissue samples) of the study. These results suggest that FFPE samples can be readily used for global N-glycome analysis holding the promise to find novel carbohydrate biomarkers in prospective and retrospective studies. Exoglycosidase based carbohydrate sequencing was also applied to reveal some basic structural information about the N-linked carbohydrates of the mouse tumor tissue samples.

Lipoxygenase-modified Ru-bpy/graphene oxide: Electrochemical biosensor for on-farm monitoring of non-esterified fatty acid

Elevated concentrations of non-esterified fatty acids (NEFA) in biological fluids are recognized as critical biomarkers for early diagnosis of dairy cow metabolic diseases. Herein, a cost-effective, electrochemically active, and bio-friendly sensor element based on ruthenium bipyridyl complex-modified graphene oxide nanosheets ([Ru(bpy)3]2+-GO) is proposed as a biosensor platform for NEFA detection. Electrochemical analysis demonstrates that the [Ru(bpy)3]2+-GO electrodes exhibit superior and durable redox properties compared to the pristine carbon and GO electrodes. Target specificity is accomplished through immobilization of the enzyme, lipoxygenase, which catalyzes the production of redox active species from NEFA. Lipoxygenases retain their catalytic ability upon immobilization and exhibit changes to amperometric signals upon interaction with various concentrations of standard NEFA and serum samples. Our study demonstrates that the [Ru(bpy)3]2+-GO electrode has the potential to serve as a biosensor platform for developing a field deployable, rapid, and user-friendly detection tool for on-farm monitoring of dairy cow metabolic diseases.

Isolation of Coxiella burnetii from serum of patients with acute Q fever

Worldwide there are few isolate collections of the intracellular bacterium Coxiella burnetii, due to the difficulties associated with working with the organism and the scarcity of suitable samples from which to attempt isolation. Particularly lacking are isolates from acute Q fever patients. The aim of this study was to evaluate whether the serum samples taken from patients with confirmed acute Q fever during the early stage of their disease represented a potential source of viable C. burnetii. Isolation was attempted from 65 of these samples by inoculation of the serum into Vero cell culture and was successful in 36 cases (55%). This high success rate was likely due to extended incubation of up to twelve weeks of the inoculated cultures, allowing the growth of the organism to levels detectable by PCR. Retrospective analysis of the time the sera was stored prior to inoculation into culture demonstrated that C. burnetii remained viable for 224days in samples stored refrigerated and 371days in samples stored frozen at −20°C. These results demonstrate that standard serum samples taken from acute Q fever patients are a valuable source of new isolates of C. burnetii, with no special handling of the specimens required to maintain the organism's viability.

Methods for the determination of glucose in blood. Part 2

The chronological development of destructive and nondestructive methods designed to determine the glucose concentration in plasma, serum, and whole blood is presented in the review. Destructive procedures are divided into spectrophotometric, spectrofluorimetric, diffraction, amperometric, potentiometric, conductometric, chromatographic, gas chromatographic-mass spectrometric, titrimetric, and calorimetric types, as well as reflectance photometry. A brief overview of these methods and the results of comparative tests are given; the procedures are systematized. It is noted that certain types of enzymatic spectrophotometric and amperometric methods have received wide acceptance for analyzes in clinical diagnostic laboratories. Outside clinical laboratories, enzymatic amperometric and spectrophotometric procedures and reflectance photometry procedures using test strips are widely used. Chromatography-mass spectrometry procedures are often applied to certify standard serum samples. Spectrofluorimetric, diffraction, and chromatographic techniques are common in scientific biomedical research. Nondestructive methods like nonenzymatic spectrophotometric, nonenzymatic amperometric, potentiometric, conductometric, titrimetric, and calorimetric procedures, as well as a number of enzymatic spectrophotometric procedures, in most cases, are not used in modern clinical and diagnostic practice.

Determination of Miglitol by Column-Switching Ion-Pair HPLC with Tris(2,2'-bipyridine)ruthenium(II)-Electrogenerated Chemiluminescence Detection.

We have developed a highly sensitive, simple method for the quantitative determination of miglitol in standard serum samples using column-switching ion-pair HPLC with tris(2,2'-bipyridine)ruthenium(II)-electrogenerated chemiluminescence detection. The serum samples were directly injected into a column-switching HPLC system with a Shim-pack MAYI-SCX precolumn to remove the serum matrix. Chromatographic separation of miglitol was achieved on a TSKgel ODS 100-V column using a mobile phase containing sodium 1-octanesulfonate as an ion-pair reagent. The detection and quantification limits of miglitol were 3 and 10 ng/mL, respectively. The calibration curve for miglitol in the serum samples showed good linearity (r(2)=0.9997) in the range of 10-2500 ng/mL. The recovery rate of miglitol from the serum samples was more than 94% as calculated from blank serum samples spiked with miglitol 50, 100, 500, 1000, and 2000 ng/mL. Therefore, this method can be applied to routine therapeutic monitoring of miglitol in serum samples.

Methods for the determination of glucose in blood. Part 1

The chronological development of destructive and nondestructive methods designed to determine the glucose concentration in plasma, serum, and whole blood is presented in the review. Destructive procedures are divided into spectrophotometric, spectrofluorimetric, diffraction, amperometric, potentiometric, conductometric, chromatographic, gas chromatographic-mass spectrometric, titrimetric, and calorimetric, as well as procedures of reflectance photometry. A brief overview of these methods and the results of comparative tests are given; the procedures are systematized. It is noted that certain types of enzymatic spectrophotometric and amperometric methods have gained wide acceptance for analyses in clinical diagnostic laboratories. Outside clinical laboratories, enzymatic amperometric and spectrophotometric procedures and reflectance photometry procedures using test strips are widely used. Chromatography-mass spectrometry procedures are often applied to certify standard serum samples. Spectrofluorimetric, diffraction, and chromatographic techniques are common in scientific biomedical research. Nondestructive methods like nonenzymatic spectrophotometric, nonenzymatic amperometric, potentiometric, conductometric, titrimetric, and calorimetric procedures, as well as a number of enzymatic spectrophotometric procedures, in most cases, are not used in modern clinical and diagnostic practice.

Time-Insensitive Fluorescent Sensor for Human Serum Albumin and Its Unusual Red Shift

The concentration of human serum albumin (HSA) indicates the health state of individuals and is routinely measured by UV spectroscopy with bromocresol. However, this method tends to overestimate HSA, and more critically, depends highly on the timing, in seconds, of the measurements. Here, we report an analog of 2′,7′-dichlorofluorescein that can be used as a fluorescent sensor to quantify HSA in human sera. The accuracy of this new method proved superior to that of bromocresol when an international standard serum sample was analyzed. This method is more convenient than the bromocresol method because it allows for fluorescence measurements during a >15 min period. Colorimetric analysis was also performed to further investigate the effects of the binding of the sensor to HSA. These spectroscopic studies suggest that absorption and emission changes upon HSA binding may be due to the dehydration of the dye and/or stabilization of the tritylic cation species.

Development of Magnetic Particle-Based Immunoassays and Their Applications in Diabetes Monitoring

In addition to blood glucose testing, monitoring of blood glycated proteins got considerable attention on the glycemic control of diabetes. Glycated albumin has been reported as a good complementary to or better indicator than glycated hemoglobin for the evaluation of short-term glycemic control. Herein, the development of magnetic particle-based immunoassays for blood glycated proteins is demonstrated. Spherical magnetic particles are fabricated composed of a polystyrene core covered with a thin layer of Fe3O4 and SiO2. The core-shell structure allow us to control a wide size range by using the polystyrene cores of different size, and the silica outer layer can be functionalized easily with silane coupling agents. Aminophenylboronic acid is covalently immobilized onto magnetic particles for the affinity isolation of glycated proteins, while horseradish peroxidase labeled antibodies are used for detection. The assays are optimized and applied successfully to the determination of glycated albumin in standard and human serum samples and show good potential as tools for diabetes monitoring.

Spectrofluorimetric determination of cefixime using terbium-danofloxacin probe.

Cefixime (Cfx), is a semi-synthetic third-generation oral cephalosporin antibiotic that is prescribed for the treatment of susceptible infections. There are some procedures for the determination of Cfx in pharmaceutical formulations and biological samples. Herein a spectrofluorimetric method was proposed for Cfx determination based on the fluorescence quenching of terbium-danofloxacin (Tb(3+)-Dano) in the presence of Cfx. Cfx was detected based on fluorescence quenching of terbium-danofloxacin (Tb(3+)-Dano) in the presence of Cfx with maximum excitation and emission wavelengths at 347 nm and 545 nm, respectively. The quenched fluorescence intensity of Tb(3+)- Dano system is proportional to the concentration of Cfx. The optimum conditions for the determination of Cfx were studied. The maximum response was achieved under optimum conditions of [Tris buffer]= 0.008 mol/l (pH 6.5), [Tb(3+)]=1×10(-4) mol/l and [Dano]=1×10(-4) mol/l. The developed method was evaluated in terms of accuracy, precision and limit of detection. The linear concentration ranges for quantification of Cfx were 8.8×10(-8)-8.8×10(-7) mol/l and 1.1×10(-7)-8.8×10(-7) mol/l in standard and human serum samples with the detection limits (S/N=3) of 2.8×10(-8) mol/l and 3.9×10(-8) mol/l, respectively. The Cfx was determined in pharmaceutical tablets and spiked serum samples and the results were satisfactory. This method is simple, practical and relatively interference-free for determination of Cfx in pharmaceutical tablets and serum samples.