Enhanced chemiluminescence enzyme‐linked immunoassay for the determination of DNA methyltransferase 1 in human serum

The occurrence of many diseases is closely related to the high expression of DNA methyltransferase 1 (DNMT1). However, most studies are focused on the detection of DNMT1 activity, a few are concerned with the detection of DNMT1 content. In this study, we developed a simple and highly sensitive chemiluminescence (CL) assay for the detection of DNMT1 content. In this method, anti‐DNMT1 monoclonal antibody was coated on a polystyrene microplate to capture DNMT1. Then anti‐DNMT1 polyclonal antibody and goat anti‐rabbit immunoglobulin G with horseradish peroxidase (IgG‐HRP) were respectively added to combine with captured DNMT1 to form a sandwich structure. Finally, the HRP could catalyze CL substrate and achieve CL signal response. Based on this novel sensitive strategy, the recovery percents were in the ranges from 71.5% to 91.0%. The precision of intra‐assays and inter‐assays were 5.45%–11.29% and 7.03%–11.25%, respectively. The method was successfully applied for the determination of DNMT1 in human serum. The detection results of serum samples showed that the proposed assay had a high correlation with enzyme‐linked immunosorbent assay (ELISA) kit. Compared with the ELISA kit (limit of detection = 0.1 ng/mL), the method has a lower limit of detection of 0.042 ng/mL. Therefore, our method has the potential for the detection of DNMT1 content in clinical diagnosis.     

Development of a chemiluminescent imaging assay for the detection of anti‐erythropoietin antibody in human sera

Measuring low amounts of anti‐erythropoietin antibodies (anti‐EPO Abs) is important to evaluate the therapeutic safety of recombinant human erythropoietin (rhEPO). In this work, a simple, sensitive and high‐throughput chemiluminescent (CL) imaging assay was developed for the detection of anti‐EPO Abs in human sera. The influence of several physicochemical parameters, such as coating conditions, incubation time, detergent concentration and exposure time, were investigated. A calibration curve was established and the range of quantitative detection was 0.12–13.91 ng/mL. The limit of detection (LOD, 3σ) for the CL‐imaging assay was 0.033 ng/mL. Compared to conventional colorimetric enzyme‐linked immunosorbent assay (ELISA), the LOD of the CL‐imaging assay is 50‐fold lower. The recoveries of anti‐EPO Abs in the fortified serum were in the range 87.1–116.9% using the present method, which highlighted the validity of the CL‐imaging assay system to accurately determine the anti‐EPO Abs in serum samples. CL‐imaging assay was used to evaluate the presence of anti‐EPO Abs in serum samples obtained from chronic renal failure (CRF) patients treated with rhEPO. Contrary to what was expected, the sera from CRF patients did not contain anti‐EPO Abs. Copyright © 2008 John Wiley & Sons, Ltd.     

Employment of 4‐(1,2,4‐triazol‐1‐yl)phenol as a signal enhancer of the chemiluminescent luminol–H2O2–horseradish peroxidase reaction for detection of hepatitis C virus in real samples

Highly sensitive detection of hepatitis C virus (HCV) in serum is a key method for diagnosing and classifying the extent of HCV infection. In this study, a p‐phenol derivative, 4‐(1,2,4‐triazol‐1‐yl)phenol (4‐TRP), was employed as an efficient enhancer of the luminol–hydrogen peroxide (H₂O₂)–horseradish peroxidase (HRP) chemiluminescence (CL) system for detection of HCV. Compared with a traditional enhancer, 4‐TRP strongly enhanced CL intensity with the effect of prolonging and stabilizing light emission. The developed CL system was applied to detecting HCV core antigen (HCV‐cAg) using a sandwich structure inside microwells. Our experimental results showed that there was good linear relationship between CL intensity and HCV‐cAg concentration in the 0.6–3.6 pg/mL range (R = 0.99). The intra‐ and inter‐assay coefficients of variation were 4.5–5.8% and 5.0–7.3%, respectively. In addition, sensitive determination of HCV‐cAg in serum samples using the luminol–H₂O₂–HRP–4‐TRP CL system was also feasible in clinical settings. Copyright © 2015 John Wiley & Sons, Ltd.     

Application of silver nanoparticles to the chemiluminescence determination of cefditoren pivoxil using the luminol–ferricyanide system

A new simple, accurate and sensitive sequential injection analysis chemiluminescence (CL) detection method for the determination of cefditoren pivoxil (CTP) has been developed. The developed method was based on the enhancement effect of silver nanoparticles on the CL signal arising from a luminol–potassium ferricyanide reaction in the presence of CTP. The optimum conditions relevant to the effect of luminol, potassium ferricyanide and silver nanoparticle concentrations were investigated. The proposed method showed linear relationships between relative CL intensity and the investigated drug concentration at the range 0.001–5000 ng/mL, (r = 0.9998, n = 12) with a detection limit of 0.5 pg/mL and quantification limit of 0.001 ng/mL. The relative standard deviation was 1.6%. The proposed method was employed for the determination of CTP in bulk drug, in its pharmaceutical dosage forms and biological fluids such as human serum and urine. The interference of some common additive compounds such as glucose, lactose, starch, talc and magnesium stearate was investigated. In addition, the interference of some related cephalosporins was tested. No interference was recorded. The obtained sequential injection analysis‐CL results were statistically compared with those from a reported method and did not show any significant differences. Copyright © 2014 John Wiley & Sons, Ltd.     

A sensitive immunoassay for determination of hepatitis B surface antigen and antibody in human serum using capillary electrophoresis with chemiluminescence detection

A sensitive and homogeneous immunoassay (IA) based on capillary electrophoresis (CE) with enhanced chemiluminescence (CL) detection has been developed for the determination of hepatitis B surface antigen (HBsAg) and antibody (HBsAb) in human serum. The conditions for the CL reaction and electrophoresis were investigated in detail using horseradish peroxidase (HRP) labeled HBsAg (HBsAg*) as a marker because of its catalytic effects on the luminol-hydrogen peroxide reaction. The CL reaction was enhanced by para-iodophenol and the CL detector was designed uniquely without any dead volume or diluents effect. The present method has been used for assaying HBsAg and HBsAb in human serum using a competitive format and a non-competitive format, respectively. Under the optimal conditions, the linear ranges were from 1 to 400 pmol/L (R=0.9988) for HBsAg and 2 to 200 mIU/mL (R=0.9981) for HBsAb. The detection limits were 0.4 pmol/L and 1 mIU/mL for HBsAg and HBsAb, respectively. The relative standard deviations of peak area were 4.2% and the errors of it were from -0.03% to +0.05% for 80 pmol/L HBsAg* (n=7). In this study, the free HBsAg* and the bound HBsAg* (HBsAg*-HBsAb) were separated in the separation capillary within 6 min using a borate run buffer. To verify the experimental reliability, the result was comparable with that of enzyme linked immunosorbent assay (ELISA) and demonstrated the feasibility of the CE-CL immunoassay method for clinical diagnosis.     

A novel chemiluminescent flow‐injection analysis of transferrin by its reduction of the luminol—hydrogen peroxide reaction catalysed by meso‐tetra‐(3‐methoxyl‐4‐hydroxyl) phenyl manganese porphyrin

Based on the inhibition effect of transferrin (Tf) on the reaction of the luminol–hydrogen peroxide (H₂O₂) chemiluminescence (CL) system, catalysed by meso‐tetra‐(3‐methoxyl‐4‐hydroxyl) phenyl manganese porphyrin (MnP) as a mimetic enzyme of peroxides, a sensitive flow‐injection CL method has been developed for the determination of Tf in an alkaline medium. The CL reaction was carefully investigated by examining the variations of reaction conditions. Under optimum conditions, the linear range for the determination of transferrin was 0.04–20.0 μg/mL and the detection limit was 1.62 ng/mL. This proposed method was sensitive, convenient and simple, and has been successfully applied to the determination of transferrin in a serum sample. Copyright © 2011 John Wiley & Sons, Ltd.     

Highly sensitive chemiluminescence determination of tenoxicam using a cerium(IV)–sodium hyposulphite system in micellar medium

A simple, rapid and precise flow‐injection–chemiluminescence (FI–CL) method is presented for the determination of tenoxicam in pharmaceutical preparations and biological samples. The method is based on the weak chemiluminescence signal arising from the reaction of cerium(IV) in a nitric acid medium with sodium hyposulphite being significantly increased by tenoxicam in the presence of sodium dodecyl benzene sulphonate. Several experimental parameters affecting the CL reaction were examined and optimized systematically. Under the optimum conditions, the CL intensity was proportional to the concentration of tenoxicam in the range 7.0 × 10^–11–5.0 × 10^–8 g/mL. The detection limit was 2.3 × 10^–11 g/mL tenoxicam and the relative standard deviation (RSD) was 2.1% for 1.0 × 10^–9 g/mL tenoxicam solution (n = 11). The proposed method was applied to the determination of tenoxicam in pharmaceutical preparations, serum and human urine, with satisfactory results. The possible mechanism of the chemiluminescence reaction is also briefly discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of phenformin hydrochloride using molecular imprinting technology coupled with flow-injection chemiluminescence

A novel method was developed using molecular imprinting technology (MIT) coupled with flow‐injection chemiluminescence (FI‐CL) for highly sensitive detection of phenformin hydrochloride (PH). The phenformin imprinted polymer was synthesized with methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross‐linker. Newly synthesized molecularly imprinted polymer (MIP) particles were packed into a column as a selective recognition element for determination of PH. A CL method for the determination of PH was developed based on the CL reaction of PH with N‐bromosuccinimide sensitized by eosin Y in basic media. The optimization of detection conditions was investigated. The CL intensity responded linearly to the concentration of PH in the range 0.09–2.0 µg/mL, with a correlation coefficient of 0.9920. The detection limit was 0.031 µg/mL. The relative standard deviation for the determination of 1.0 µg/mL PH solution was 1.0% (n = 11). The method was applied to the determination of PH in urine samples, with satisfactory results. Copyright © 2011 John Wiley & Sons, Ltd.     

Chemiluminescence determination of bromhexine hydrochloride with morin as chemiluminescent reagent

A new chemiluminescence (CL) reaction was observed when cerium(IV) solution was injected into bromhexine hydrochloride–morin solution. Based on this, a flow‐injection CL method for the determination of bromhexine hydrochloride was established. A possible mechanism of the CL reaction was proposed via the investigation of the CL kinetic characteristics, the CL spectrum and the fluorescence spectra of some related substances. Under optimum conditions, the CL signal was correlated linearly with concentration of bromhexine hydrochloride over the range 2.0 × 10^–9–2.0 × 10^–7 g/mL, with a linear correlation of 0.9995. The detection limit was 9 × 10^–10 g/mL bromhexine hydrochloride and the relative standard deviation was 1.0% (c = 2.0 × 10^–8 g/mL bromhexine hydrochloride, n = 11). The method was applied to the determination of bromhexine hydrochloride in pharmaceutical preparations and human urine samples with satisfactory results. Copyright © 2008 John Wiley & Sons, Ltd.     

Determination of diethylstilbestrol based on biotin–streptavidin‐amplified time‐resolved fluoro‐immunoassay

A rapid and sensitive time‐resolved fluoroimmunoassay (TR–FIA) based on the biotin–streptavidin amplification system was developed for the determination of diethylstilbestrol (DES). Europium‐labelled streptavidin derivatives combined with europium and anhydride of diethylene triamine penta‐acetic acid were used to label streptavidin; biotin was coupled with goat anti‐rabbit IgG to form a biotin–goat anti‐rabbit IgG bridge between streptavidin–europium and the anti‐DES antibody in the immunoassay. The DES assay was carried out by measuring the fluorescence of Eu³⁺–SA at 615 nm. The presented method produced a wide linear range, 0.001–1000.0 ng/mL, and a detection limit up to 0.81 pg/mL for DES. The method was applied to determine DES in serum samples, with recoveries of 97.4–107.8% and RSD 1.32–4.04%. The assay results by the present method showed that biotin–streptavidin amplified TR–FIA for DES detection; it may offer high sensitivity and promising alternative special methods in biological samples. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of estradiol valerate in pharmaceutical preparations and human serum by flow injection chemiluminescence

A novel method for the detection of trace estradiol valerate (EV) in pharmaceutical preparations and human serum was developed by inhibition of luminol chemiluminescence (CL) by estradiol valerate on the zinc deuteroporphyrin (ZnDP)‐enhanced luminol‐K₃Fe(CN)₆ chemiluminescence system. Under optimized experimental conditions, CL intensity and concentration of estradiol valerate had a good linear relationship in the ranges of 8.0 × 10^‐8 to 1.0 × 10^‐5 g/mL. Detection limit (3σ) was estimated to be 3.5 × 10^‐8 g/mL. The proposed method was applied successfully for the determination of estradiol valerate in pharmaceutical preparations and human serum and recoveries were 97.0‐105.0% and 95.5‐106.0%, respectively. The possible mechanism of the CL system is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of lophine derivatives as L‐012 (luminol analog)‐dependent chemiluminescence enhancers for measuring horseradish peroxidase and H2O2

8‐Amino‐5‐chloro‐7‐phenylpyrido[3,4‐d]pyridazine‐1,4(2H,3H)dione (L‐012) was recently synthesized as a new chemiluminescence (CL) probe; the light intensity and the sensitivity of L‐012 are higher than those of other CL probes such as luminol. Previously, our group developed four lophine‐based CL enhancers of the horseradish peroxidase (HRP)‐catalyzed CL oxidation of luminol, namely 2‐(4‐hydroxyphenyl)‐4,5‐diphenylimidazole (HDI), 2‐(4‐hydroxyphenyl)‐4,5‐di(2‐pyridyl)imidazole (HPI), 4‐(4,5‐diphenyl‐1H‐imidazol‐2‐yl)phenylboronic acid (DPA), and 4‐[4,5‐di(2‐pyridyl)‐1H‐imidazol‐2‐yl]phenylboronic acid (DPPA), and showed that DPPA was suitable for the photographic detection of HRP. In this study, we replaced luminol with L‐012 and evaluated these as L‐012‐dependent CL enhancers. In addition, to detect HRP and/or H₂O₂ with higher sensitivity, each detection condition for the L‐012–HRP–H₂O₂ enhanced CL was optimized. All the derivatives enhanced the L‐012‐dependent CL as well as luminol CL; HPI generated the highest enhanced luminescence. Under optimized conditions for HRP detection, the detection limit of HRP was 0.08 fmol. By contrast, the detection limit of HRP with the enhanced L‐012‐dependent CL using 4‐iodophenol, which is a common enhancer of luminol CL, was 1.1 fmol. With regard to H₂O₂ detection, the detection limits for enhanced CL with HPI and 4‐iodophenol were 0.29 and 1.5 pmol, respectively. Therefore, it is demonstrated that HPI is the most superior L‐012‐dependent CL enhancer. Copyright © 2013 John Wiley & Sons, Ltd. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of carbamazepine in human urine and serum samples by high‐performance liquid chromatography with post‐column Ru(bipy)‐Ce(SO4)2 chemiluminescence detection

A novel, sensitive and rapid CL method coupled with high‐performance liquid chromatography separation for the determination of carbamazepine is described. The method was based on the fact that carbamazepine could significantly enhance the chemiluminescence of the reaction of cerium sulfate and tris(2,2‐bipyridyl) ruthenium(II) in the presence of acid. The chromatographic separation was performed on a Kromasil® (Sigma‐Aldrich) TM RP‐C18 column (id: 150 mm × 4.6 mm, particle size: 5 µm, pore size: 100 Å) with a mobile phase consisting of methanol–water‐glacial acetic acid (70:29:1, v/v/v) at a flowrate of 1.0 mL/min, the total analysis time was within 650 s. Under optimal conditions, CL intensity was linear for carbamazepine in the range 2.0 × 10^?8 ~ 4.0 × 10^?5 g/mL, with a detection limit of 6.0 × 10^?9 g/mL (S/N = 3) and the relative standard detection was 2.5% for 2.0 × 10^?6 g/mL (n = 11). This method was successfully applied to the analysis of carbamazepine in human urine and serum samples. The possible mechanism of the CL reaction is also discussed briefly. Copyright © 2012 John Wiley & Sons, Ltd.     

Determination of sulpiride in pharmaceutical preparations and biological fluids using a Cr (III) enhanced chemiluminescence method

A highly sensitive and simple method for identifying sulpiride in pharmaceutical formulations and biological fluids is presented. The method is based on increased chemiluminescence (CL) intensity of a luminol–H₂O₂ system in response to the addition of Cr (III) under alkaline conditions. The CL intensity of the luminol–H₂O₂–Cr (III) system was greatly enhanced by the addition of sulpiride and the CL intensity was proportional to the concentration of sulpiride in a sample solution. Various parameters affecting the CL intensity were systematically investigated and optimized for determination of the sulpiride in a sample. Under the optimum conditions, the CL intensity was proportional to the concentration of sulpiride in the range of 0.068–4.0 µg/mL, with a good correlation coefficient of 0.997. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 8.50 × 10^‐6 µg/mL and 2.83 × 10^‐5 µg/mL, respectively. The method presented here produced good reproducibility with a relative standard deviation (RSD) of 2.70% (n = 7). The effects of common excipients and metal ions were studied for their interference effect. The method was validated statistically through recovery studies and successfully applied for the determination of sulpiride in pure form, pharmaceutical preparations and spiked human plasma samples. The percentage recoveries were found to range from 99.10 to 100.05% for pure form, 98.12 to 100.18% for pharmaceutical preparations and 97.9 to 101.4% for spiked human plasma. Copyright © 2012 John Wiley & Sons, Ltd.     

Chemiluminescence determination of promazine in human serum and drug formulations using Ru(phen)32+–Ce(IV) system and a chemometrical optimization approach

A new chemiluminescence (CL) method using flow injection has been described for the rapid and sensitive determination of promazine hydrochloride (PMH). The method is based on the CL reaction of PMH with tris(1,10 phenanthroline)ruthenium(II), [Ru(phen)₃²⁺] and Ce(IV) in sulfuric acid medium. Effects of chemical variables were investigated employing central composite design and response surface methodology. Under the optimum conditions, the CL intensity was proportional to the concentration of the drug in solution over the ranges 0.020–0.32 and 0.32–32 µg/mL. The limit of detection (signal‐to‐noise ratio = 3) was 0.012 µg/mL. The method was applied successfully to the determination of PMH in drug formulations and human serum (recovery percentages between 96.7 and 105.0%). The relative standard deviation for 11 replicate determinations of 1.5 µg/mL of PMH was 1.7%. The minimum sampling rate was 100 samples per hour. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of ferulic acid by flow injection chemiluminescence analysis based on enhancement of the N‐bromobutanimide–eosin–CrCl3 system in alkaline solution

A simple and sensitive flow injection chemiluminescence method has been developed for the determination of ferulic acid (FA) based on the significant enhancement effect of FA on the CL signal of the N‐bromobutanimide (NBS)–eosin–CrCl₃ system in alkaline solution. Under optimum conditions, the enhanced CL intensity is linearly related to the concentration of FA in its pharmaceutical preparations and human plasma samples. The corresponding linear regression equations were established over the 4.0 × 10^–10–1.0 × 10^–7 g/mL for FA tablets and 2.0 × 10^–10–1.0 × 10^–7 g/mL for plasma samples. The limit of detection for FA tablets and limit of quantification for plasma samples were 2.8 × 10^–10 g/mL (3 σ) and 3.04 × 10^–10 g/mL (10 σ), respectively. A complete analysis could be performed within 40 s, including washing and sampling, giving a throughput of ≈90/h. The proposed method was successfully applied to the determination of FA in pharmaceutical preparations and human plasma samples with satisfactory results. The recoveries of pharmaceutical preparations and human plasma samples at three different concentrations were 97.8–102.6% and 96.7–104.0%, respectively. Furthermore, the possible mechanism of CL reactions was also discussed briefly. Copyright © 2013 John Wiley & Sons, Ltd.     

A label‐free immunoassay using eggshell membrane as matrix and poly(diallyldimethylammonium chloride) as light‐scattering enhancer

A label‐free immunoassay system using eggshell membrane as a matrix was developed. A common spectrofluorometer was used to collect light‐scattering signals. The rabbit anti‐human IgG (Ab) was first immobilized on the eggshell membrane with glutaraldehyde. Then, based on the immunoreactions and electrostatic interaction, the target human IgG antigen (Ag) and poly(diallyldimethylammonium chloride) (PDDA) were captured on the eggshell membrane. It was found that the light‐scattering signal resulting from the PDDA immunotargeted on modified eggshell membrane was related to the concentration of target antigen. Under the optimal conditions, the light scattering intensity is directly proportional to the concentration of Ag in the range of 5.00–500 ng/mL (r = 0.995) with the limit of detection of 2.31 ng/mL [signal:noise ratio (S:N) = 3]. The proposed method was successfully applied to the determination of IgG in human serum, and the results were in agreement with those obtained by a general immunonephelometric method. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of a high‐throughput,indirect antibody immobilization format chemiluminescence enzyme immunoassay (CLEIA) for the determination of progesterone in human serum

A high‐throughput and simple chemiluminescence (CL) enzyme immunoassay (CLEIA) for the determination of progesterone (P) in human serum was developed, with the highly sensitive 4‐methoxy‐4‐(3‐phosphatephenyl)‐spiro‐(1,2‐dioxetane‐3,2′‐adamantane) (AMPPD)–alkaline phosphatase (ALP) system as the CL detection system. The results showed that the indirect immobilization of rabbit anti‐progesterone polyclonal antibody (RAPA) through secondary antibody exhibited apparent advantages over direct coating in terms of antibody saving and improvement of the coating stability and uniformity. The direct analysis of P in human serum without extraction was realized by using 8‐anilino‐1‐naphthalenesulphonic acid (ANS) to displace P from its binding proteins. The effect of several relevant parameters of the immunoreaction were examined and optimized. Compared with some commercial progesterone kits, the presented CLEIA has higher sensitivity with detection limitation as low as 0.06 ng/mL. The recoveries were 95.9–101%. The coefficient of variation was <8.4% and 9.9% for intra‐ and inter‐assay precision, respectively. This method has been successfully applied to the evaluation of P in human serum. Copyright © 2008 John Wiley & Sons, Ltd.     

Determination of fluvoxamine maleate in human urine and human serum using alkaline KMnO4–rhodamine B chemiluminescence

The flow‐injection chemiluminescence (FI‐CL) behavior of a gold nanocluster (Au NC)–enhanced rhodamine B–KMnO₄ system was studied under alkaline conditions for the first time. In the present study, the as‐prepared bovine serum albumin‐stabilized Au NCs showed excellent stability and reproducibility. The addition of trace levels of fluvoxamine maleate (Flu) led to an obvious decline in CL intensity in the rhodamine B–KMnO₄–Au NCs system, which could be used for quantitative detection of Flu. Under optimized conditions, the proposed CL system exhibited a favorable analytical performance for Flu determination in the range 2 to 100 μg ml^?1. The detection limit for Flu measurement was 0.021 μg ml^?1. Moreover, this newly developed system revealed outstanding selectivity for Flu detection when compared with a multitude of other species, such as the usual ions, uric acid and a section of hydroxy compounds. Additionally, CL spectra, UV–visible spectroscopes and fluorescence spectra were measured in order to determine the possible reaction mechanism. This approach could be used to detect Flu in human urine and human serum samples with the desired recoveries and could have promising application under physiological conditions.     

Effect of colloidal β-cyclodextrins-Fe(3) O(4) magnetic nanoparticles on the chemiluminescence enhancement of luminol-Ag(III) complex for rapid and sensitive determination of cysteine in human serum

Colloidals solution of Fe₃O₄ magnetic nanoparticles (MNPs), capped with β‐cyclodextrins (β‐CD) as inclusion complexes, were found to enhance the chemiluminescence (CL) intensity of the luminol–diperiodatoargentate(III) (DPA) system. On injection of cysteine into the luminol–DPA–β‐CD–Fe₃O₄ MNPs inclusion complexes system, the CL intensity is strongly enhanced. The enhanced CL signal is ascribed to the catalytic effect of Fe₃O₄ MNPs capped with β‐CD, which is assumed to stabilize the CL intermediate. Based on these findings, a rapid and sensitive assay was developed for the determination of cysteine in human serum. The effects of analytical variables on the CL signal were studied and optimized. Under the optimum conditions, the CL intensity was directly proportional to the concentration of cysteine in the range 8.0 × 10^–9–1.0 × 10^–6 mol/L. The detection limit was 2.8 × 10^–9 mol/L (3 S_b/m) and the relative standard deviation (RSD) for 10 replicate determinations of 1.0 × 10^–7 mol/L cysteine was 3.5%. The proposed method was applied to the sensitive determination of cysteine in human serum samples, and compared with the Ellman method with satisfactory results. Copyright © 2011 John Wiley & Sons, Ltd.