A simple and cost-effective sensing strategy of mercury (II) based on analyte-inhibited aggregation of gold nanoparticles

A simple, cheap and ultrasensitive colorimetric Hg2+ sensing strategy has been developed in this paper. It was based on a special 'Hg2+-inhibited aggregation' mechanism, in which the pyridine-induced aggregation of unmodified gold nanoparticles (AuNPs) could be inhibited upon addition of Hg2+. Compared with the previous Hg2+-induced aggregation mechanism, the new design just employed a cheap and facile chemical reagent, pyridine, as an inducer of aggregation of AuNPs and elimination of the modifying or labeling step. The effects of pyridine concentration and size of AuNPs were investigated. The calibration curve showed that the extinction ratio value at 525 and 700 nm increased linearly over the Hg2+ concentration range of 0.15-3.00 μM with a detection limit of 55 nM. The specificity of this sensor is remarkably high over that of the other metal ions without adding any masking agent.     

Blue-to-red colorimetric sensing strategy for Hg²⁺ and Ag⁺ via redox-regulated surface chemistry of gold nanoparticles

Here we report a "blue-to-red" colorimetric method for determination of mercury ions (Hg2?) and silver ions (Ag?) based on stabilization of gold nanoparticles (AuNPs) by redox formed metal coating in the presence of ascorbic acid (AA). AuNPs were first stabilized by Tween 20 in phosphate buffer solution with high ionic strength. In a target ion-free system, the addition of N-acetyl-L-cysteine resulted in the aggregation of Tween 20 stabilized AuNPs for mercapto ligand self-assembled on the surface of AuNPs, which induced the AuNPs to be unstable. This would lead to a color change from red to blue. By contrast, in an aqueous solution with Hg2? or Ag?, the ions could be reduced with the aid of AA to form Hg-Au alloy or Ag coating on the surface of AuNPs. This metal coating blocked mercapto ligand assembly and AuNPs kept monodispersed after addition of N-acetyl-L-cysteine, exhibiting a red color. Therefore, taking advantage of this mechanism, a "blue-to-red" colorimetric sensing strategy could be established for Hg2? and Ag? detection. Compare with the commonly reported aggregation-based method ('red-to-blue'), the color change from blue to red seems more eye-sensitive, especial in low concentration of target. Moreover, selective analysis of Hg2? and Ag? was simply achieved by the redox nature of target ions and the application of classic ion masking agents, avoiding the design and selection of ion chelating moieties and complicated gold surface modification procedure. This method could selectively detect Hg2? and Ag? as low as 5 nM and 10 nM in pure water with a linear range of 5 × 10?? to 1 × 10?? M for Hg2? and 1 × 10?? to 8 × 10?? M for Ag?, respectively. It was successfully applied to determination of Hg2? and Ag? in tap water and drinking water.     

Lead (II) ion detection in surface water with pM sensitivity using aza-crown-ether-modified silver nanoparticles via dynamic light scattering

In this paper, we reported ultrasensitive lead ion detection in environmental water with pM sensitivity using aza-crown-ether-modified silver nanoparticles (ACE-Ag NPs) through dynamic light scattering (DLS). The colorimetric method based on ACE-Ag NPs is not capable of detecting Pb2+ ions over other metal ions (Fe3+, Co2+, Cu2+, Hg2+, Cd2+, Ag+, Li+, Na+, K+ and Cs+) with high sensitivity. But DLS has improved the selectivity and sensitivity of the Pb2+ detection system (50-fold or more) over colorimetric method, and its detection limit is 0.25 pM (1.03 ppt). The Pb2+ DLS assay can be applied to detect Pb2+ in the environmental water, such as in Yangtze and East Lake water samples with a detection limit of 0.20 and 0.22 pM, which is much lower than the maximum contamination level of 4.8×10(-8) M for lead in surface water defined by the national environmental quality standards of China (GB 3838-2002). Also, this method has a good performance in the determination of Pb2+ in drinking water, which is much lower than the maximum contamination level (MCL) of 72 nM for lead as defined by the US Environmental Protection Agency (EPA).     

Detection of Hg2+ using microcantilever sensors

Trace amounts of Hg2+ are detected by using a microcantilever coated with gold. The microcantilever undergoes bending due to accumulation of Hg2+ on the gold surface. It is found that a concentration of 10(-11) M Hg2+ can be detected using this technology. Other cations, such as K+, Na+, Pb2+, Zn2+, Ni2, Cd2+, Cu2+, and Ca2+ have little or no effect on the deflection of the cantilever. The selectivity of the Hg2+ sensor could be improved by coating the gold surface of microcantilever with a self-assembled monolayer of a long-chain thiol compound.     

A novel heterogeneous colorimetric and spectrophotometric chemosensor for detection and adsorption of Hg0 and Hg2+

Functionalized mesoporous silica with an immobilized azobenzene-coupled receptor 1 (FMS-1) as heterogeneous "naked-eye" colorimetric and spectrophotometric chemosensor was prepared by sol-gel reaction. The optical sensing ability of FMS-1 was studied by addition of metal ions such as K+, Ca2+, Sr2+, Co2+, Cd2+, Pb2+, Zn2+, Fe3+, Cu2+ and Hg2+ in aqueous solution. Interestingly, upon the addition of Hg2+ in aqueous suspension, FMS-1 resulted in a color change from maroon to red within 10 s. On the other hand, no significant color changes were observed with the other metal ions. These findings confirm that FMS-1 can be useful as a chemosensor for selective detection of Hg2+ over a range of metal ions. Furthermore, the adsorption ability of the FMS-1 was also estimated by measuring the amount of Hg2+ and Hg0 adsorbed on the FMS-1, resulting in 95% for Hg2+ and 75% for Hg0, respectively, suggesting that the FMS-1 is potentially useful as the adsorbent for separation of Hg0 and Hg2+ in chromatography.     

Determination of methylmercury, ethylmercury, and inorganic mercury in mouse tissues, following administration of thimerosal, by species-specific isotope dilution GC-inductively coupled plasma-MS

Isotopically enriched HgO standards were used to synthesize CH3(200)Hg+ and C2H5(199)Hg+ using Grignard reagents. These species were employed for isotope dilution GC-ICPMS to study uptake and biotransformation of ethylmercury in mice treated with thimerosal, (sodium ethylmercurithiosalicylate) 10 mg L(-1) in drinking water ad libitum for 1, 2.5, 6, or 14 days. Prior to analysis, samples were spiked with aqueous solutions of CH3(200)Hg+, C2H5(199)Hg+, and 201Hg2+ and then digested in 20% tetramethylammonium hydroxide and extracted at pH 9 with DDTC/toluene. Extracted mercury species were reacted with butylmagnesium chloride to form butylated derivatives. Absolute detection limits for CH3Hg+, C2H5Hg+, and Hg2+ were 0.4, 0.2, and 0.6 pg on the basis of 3sigma of five separate blanks. Up to 9% of the C2H5Hg+ was decomposed to Hg2+ during sample preparation, and it is therefore crucial to use a species-specific internal standard when determining ethylmercury. No demethylation, methylation, or ethylation during sample preparation was detected. The ethylmercury component of thimerosal was rapidly taken up in the organs of the mice (kidney, liver, and mesenterial lymph nodes), and concentrations of C2H5Hg+ as well as Hg2+ increased over the 14 days of thimerosal treatment. This shows that C2H5Hg+ in mice to a large degree is degraded to Hg2+. Increased concentrations of CH3Hg+ were also observed, which was found to be due to impurities in the thimerosal.     

Colorimetric determination of melamine by pyridine-3-boronic acid modified gold nanoparticles

A rapid, simple and sensitive colorimetric detection method for melamine was proposed based on pyridine-3-boronic acid (PBA) modified gold nanoparticles (AuNPs). The formation of supramolecular hydrogen-bonded structure between PBA and melamine resulted in the aggregation of PBA modified AuNPs and the color change from red to blue. Melamine could be detected by colorimetric response of AuNPs that could be detected by naked eyes or a UV-vis spectrophotometer. The detection concentration of melamine ranged from 6.0 x 10(-8) to 1.6 x 10(-6) M, and the detection limit (3sigma) was 3.0 x 10(-8) M (i.e., 3.2 ppb). This provided an effective and facile colorimetric sensor for real-time and on-site determination of melamine. Particularly, the proposed method could be used to detect melamine in pretreated liquid milk products with high sensitivity and low interference, and the recoveries were from 95% to 102%.     

Mercuric ion sensing by a film bulk acoustic resonator

This paper describes a film bulk acoustic resonator (FBAR) mass sensor for detecting Hg2+ ion in water with excellent sensitivity and selectivity. When a thin Au film was deposited on the surface of an FBAR, the resonant frequency shifted to a lower value when the film was exposed to Hg2+ in aqueous solution. The FBAR sensor detected as low as 10(-9) M Hg2+ (0.2 ppb Hg2+) in water. Other ions such as K+, Ca2+, Mg2+, Zn2+, and Ni2+ had little or no effect on the resonant frequency of the FBAR. Coating of the FBAR Au surface with a self-assembled monolayer (SAM) of 4-mercaptobenzoic acid decreased the Hg2+ response.     

Chemiluminescence catalysed by gold nanoparticles for the analysis of arsenic (III) in real water

A gold nanoparticle (AuNPs)-catalysed chemiluminescence (CL) method is developed for the analysis of As³⁺ cations by detecting the enhancement of the luminol–H₂O₂ reaction by AuNPs. AuNPs of different sizes were prepared by a chemical method. The size and shape of these nanoparticles were determined by transmission electron microscopy. The various parameters of the reaction media such as the pH and the concentration of H₂O₂ and luminol were optimised. The enhancement of the CL intensity may be as a result of energy transfer by the AuNPs or plasmon-induced enhancement. The interaction of the AuNPs with As³⁺ amplified the CL signal. This amplified CL was used to detect As³⁺ in real water samples. The linear region of the calibration curve from 0.3 to 4 µg/L shows that this is a suitable method for the detection of low concentrations of arsenic (III).     

Species-specific isotope dilution with permeation tubes for determination of gaseous mercury species

Instrumentation and methodology for determination of the gaseous mercury species Hg0, (CH3)2Hg, and CH3Hg+ has been developed. The method is based on continuous addition of gaseous isotopically enriched Hg species (tracers) at the point of sample acquisition, in combination with reduced pressure sampling on Carbotrap adsorbent tubes. Permeation tubes are used for generation of the tracers. Collected species are thermally desorbed and purged through an aqueous sodium tetraethylborate solution for derivatization of CH3Hg+. The purged gas is dried with a Nafion membrane, and the Hg species are subsequently collected on a smaller Tenax TA adsorbent tube. Species are then thermally desorbed from the Tenax TA and introduced into a gas chromatograph connected to an inductively coupled plasma mass spectrometer for separation and detection. To be able to add tracers during field sampling, we developed a portable device, supplying the permeation tubes with a thermostated and mass flow-controlled air stream of 5.0 +/- 0.1 degrees C and 50.0 mL min(-1), respectively. Typical permeation rates obtained during a period of more than 6 weeks were 12.93 +/- 0.56, 0.42 +/- 0.01, and 0.49 +/- 0.03 (mean +/- standard deviation) pg of Hg min(-1) for a set of 199Hg0, (CH3)2 198Hg, and CH3 200Hg+ tubes, respectively. Methodological detection limits (3sigma) were determined to 700 pg of Hg m(-3) for Hg0 and 50 pg of Hg m(-3) for (CH3)2Hg and CH3Hg+. The collection efficiencies for sampled volumes of 400 L of synthetic air on the Carbotrap tubes used in this study were 13 +/- 2, 102 +/- 2, and 99 +/- 4% for Hg0, (CH3)2Hg, and CH3Hg+, respectively. Desorption efficiencies for the above species and tubes were 98 +/- 2, 98 +/- 1, and 90 +/- 4%, respectively. Fractions (20-40%) of the added (CH3)2 198Hg and CH3 200Hg+ tracers were found to be transformed during the analytical processing of collected air samples. Determined concentrations in the research laboratory air, corrected for species transformations, were 3-53, 8-11, and 1-2 ng of Hg m(-3) for Hg0, (CH3)2Hg, and CH3Hg+, respectively. Concentrations in the ambient air were determined to be 2.1-2.6 ng m(-3) for Hg0 and below the detection limit for (CH3)2Hg and CH3Hg+.     

Factors influencing redox magnetohydrodynamic-induced convection for enhancement of stripping analysis

Factors affecting the use of redox magnetohydrodynamics (MHD) to enhance the stripping analysis response to heavy metals have been investigated. The analytes were Pb2+, Cd2+, Cu2+, and Tl+ at concentrations ranging from 5 nM to 2 microM. Co-deposition of analytes with Hg2+ (to form a thin Hg film electrode) occurs along with reduction of a high concentration of Fe3+. The Fe3+ provides the high cathodic current necessary to produce a significant Lorentz force, and therefore enhanced convection and larger stripping signals and sensitivities, when the analysis is performed in the presence of an external magnetic field. The effects of varying Fe3+ concentration (1-100 mM), working electrode size (10 microm-3 mm), and magnetic field strengths (0-1.77 T) generated with electromagnets and NdFeB permanent magnets were investigated. Using 100 mM Fe3+ as the MHD-generating redox species at a 3-mm working electrode and in a magnetic field of 1.77 T, peak areas from linear sweep voltammetry were increased by as much as 159 +/- 5%, compared to the signal obtained in the absence of a magnetic field. Experimental detection limits as low as 5 nM were achieved with only a 1-min preconcentration time. A field strength as low as 0.12 T offers some signal enhancement with 100 mM Fe3+. While linear scan anodic stripping voltammetry was used primarily to obtain the signals after the deposition step, potentiometric stripping analysis was also investigated. Redox MHD is an attractive alternative convection method for applications involving sample volumes too small for mechanical stirring or for in-field applications using portable devices that cannot be complicated by the instrumentation required for mechanical stirring.     

Characterization of an EDTA bonded conducting polymer modified electrode: its application for the simultaneous determination of heavy metal ions

An EDTA bonded conducting polymer modified electrode (EDTA-CPME) was fabricated by polymerization of 3',4'-diamino-2,2';5',2'-terthiophene monomer on a GCE, followed by the reaction with EDTA in the presence of catalyst. The surface of the resulting modified electrode was characterized with EQCM, ESCA, SEM, Auger electron spectroscopy, scanning Auger microscopy, and electrochemical methods. The amounts of polymer and EDTA attached on the polymer film were determined. Simple immersing of the EDTA-CPME into a sample solution led to the chemical deposition through the complexation with Pb2+, Cu2+, and Hg2+ ions, simultaniously. Various experimental parameters that affect the simultaneous analysis of the metal ions, e.g., EDTA amount, pH, deposition time, and deposition temperature, were optimized. Calibration plots for the EDTA-CPME with square wave voltammetry were obtained in the concentration range between 5.0 x 10(-10) and 1.0 x 10(-7) M for Cu(II) and between 7.5 x 10(-10) and 1.0 x 10(-7) M for Pb(II) and Hg(II). The detection limits for Pb(II), Cu(II), and Hg(II) ions were determined to be about 6.0 x 10(-10), 2.0 x 10(-10), and 5.0 x 10(-10) M, respectively. Interference effects from other metal ions were studied at various pHs and it was found that there was little or no effect on the simultaneous determination. The stability of the EDTA-CPME was remarkably improved by coating the surface with the Nafion film, and the electrode can be used for more than one month. Analytical availability of the EDTA-CPME was demonstrated by the application for the certified standard urine reference material and tap water.     

Photoelectrochemical oxidation of DNA by ruthenium tris(bipyridine) on a tin oxide nanoparticle electrode

Selective photoelectrochemical oxidation of DNA was achieved by ruthenium tris(bipyridine) immobilized on a tin oxide nanoparticle electrode. The metal complex was covalently attached to a protein, avidin, which adsorbed strongly on the tin oxide electrode by electrostatic interaction. Upon irradiation with 473-nm light, anodic photocurrent was generated in a blank electrolyte and was enhanced significantly after addition of poly(guanadylic acid) (poly-G) into the electrolyte. The current increased progressively with the nucleotide concentration, suggesting the enhancement effect was related to poly-G. The action spectrum indicates that the photocurrent was initiated by light absorption of the ruthenium compound immobilized on the electrode. Among the various polynucleotides examined, poly-G produced the largest photocurrent increase, followed by poly-A, single-stranded DNA, chemically damaged DNA, and double-stranded DNA, whereas poly-C and poly-U showed little effect. The combined experimental data support the hypothesis that the photoexcited Ru2+ species injects an electron into the semiconductor and produces Ru3+, which is then reduced back to Ru2+ by guanine and adenine bases in DNA, resulting in the recycling of the metal complex and enhanced photocurrent. The photoelectrochemical reaction can be employed as a new method for the detection of DNA damage.     

PVC membrane potentiometric sensor based on 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthroline-phane for selective determination of neodymium(III)

Spectrofluorometric studies on the binding properties of 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthrolinephane (L) toward La3+, Sm3+, Gd3+, Yb3+, and Nd3+ in methanol solution revealed the occurrence of both 1:1 and 2:1 (ligand/metal) complexation with a stability order of Nd3+ > Yb3+ > Gd3+ > Sm3+ > La3+. Consequently, L was used as a suitable neutral ionophore for the preparation of a novel polymeric membrane-selective electrode for Nd3+ ion. The electrode exhibited a Nernstian response over a wide concentration range (1.0 x 10(-6)-1.0 x 10(-2) M) with a low limit of detection of 7.9 x 10(-7) M. The electrode possesses a fast response time of <5 s and can be used for at least 9 weeks without observing any considerable deviation. The proposed electrode revealed a very good selectivity for Nd3+ over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, including members of the lanthanide family other than Nd3+. The potentiometric response of the electrode is independent of the pH of test solution in the pH range 4.0-6.5. The proposed electrode was successfully applied to the recovery of Nd3+ ion from tap water samples and, also, as an indicator electrode, in potentiometric titration of neodymium(III) ions.     

On-site analysis of arsenic in groundwater using a microfabricated gold ultramicroelectrode array

Rapid on-site analysis of arsenic in groundwater was achieved with a small battery-powered unit in conjunction with a microfabricated gold ultramicroelectrode array (Au-UMEA). The sensor, consisting of 564 UME disks with a unique gold surface created by electron beam evaporation, was demonstrated to be highly sensitive to low-ppb As3+ using square wave anodic stripping voltammetry. The influence of the square wave frequency, pulse amplitude, and deposition potential on the arsenic peak stripping current was investigated. Varying those theoretical parameters yielded results surprisingly similar to those for the thin Hg film case. The performance of the Au-UMEA was evaluated for reproducibility and reliability. Three stability tests showed an average relative standard deviation of 2.5% for 15 consecutive runs. Limits of detection were investigated, and 0.05 ppb As3+ could be measured while maintaining a S/N of 3:1. Interference studies were performed in the presence of 50-500 ppb of Cu2+, Hg2+, and Pb2+. On-site analysis of groundwater containing arsenic was performed with a small battery-powered potentiostat. Quantification was done through standard additions, and these results were compared to the standard EPA methodology.     

Highly selective colorimetric detection of hydrochloric acid using unlabeled gold nanoparticles and an oxidizing agent

We report a colorimetric system for the detection of HCl in aqueous environments using unlabeled gold nanoparticle (AuNP) probes. This nonaggregation-based detection system relies on the ability of chloro species to cause rapid leaching of AuNPs in an aqueous dispersion containing a strong oxidizing agent, such as HNO(3) or H(2)O(2). The leaching process leads to remarkable damping of the surface plasmon resonance peak of the AuNP dispersion. This method works only with AuNPs of a particular size (～30 nm diameter). It is highly selective for HCl over several common mineral acids, salts, and anions. This simple and cost-effective sensing system provides rapid and simple detection of HCl at concentrations as low as 500 ppm (far below the hazard limit) in natural water systems.     

Enzymatic cleavage of nucleic acids on gold nanoparticles: a generic platform for facile colorimetric biosensors

The enzymatic cleavage of nucleic acids (DNA or DNA with a single RNA linkage) on well-dispersed gold nanoparticles (AuNPs) is exploited in the design of facile colorimetric biosensors. The assays are performed at salt concentrations such that DNA-modified AuNPs are barely stabilized by the electrostatic and steric stabilization. Enzymatic cleavage of DNA chains on the AuNP surface destabilizes the AuNPs, resulting in a rapid aggregation driven by van der Waals attraction, and a red-to-purple color change. Two different systems are chosen, DNase I (a DNA endonuclease) and 8-17 (a Pb(2+)-depedent RNA-cleaving DNAzyme), to demonstrate the utility of our assay for the detection of metal ions and sensing enzyme activities. Compared with previous studies in which AuNP aggregates are converted into dispersed AuNPs by enzymatic cleavage of DNA crosslinkers, the present assay is technically simpler. Moreover, the accessibility of DNA to biomolecular recognition elements (e.g. enzymes) on well-dispersed AuNPs in our assay appears to be higher than that embedded inside aggregates. This biosensing system should be readily adaptable to other enzymes or substrates for detection of analytes such as small molecules, proteases and their inhibitors.     

Ultrasensitive sensing of Hg(2+) and CH(3)Hg(+) based on the fluorescence quenching of lysozyme type VI-stabilized gold nanoclusters

This study presents a one-step approach to prepare lysozyme type VI-stabilized gold nanoclusters (Lys VI-AuNCs) for the ultrasensitive detection of Hg(2+) and CH(3)Hg(+) based on fluorescence quenching. The optical properties and size of Lys VI-AuNCs are highly dependent on the concentration of Lys VI, which acts as both a reducing and a stabilizing agent. With an increase in the concentration of Lys VI, we observed a systematic blue shift in the fluorescence maxima, an increase in the quantum yields, and a reduction in the particle size. When using 25 mg/mL Lys VI as a reducing agent, the formed Lys VI-AuNCs (denoted as Au-631) were found to be highly stable in a high-concentration glutathione or NaCl. Additionally, the Au-631 were capable of sensing Hg(2+) and CH(3)Hg(+) through the interaction between Hg(2+)/CH(3)Hg(+) and Au(+) on the Au surface; the limits of detection (LODs) for Hg(2+) and CH(3)Hg(+) were 3 pM and 4 nM, respectively. The selectivity of this probe is more than 500-fold for Hg(2+) over any metal ions. As compared to bovine serum albumin-stabilized AuNCs, Au-631 provided an approximately 330-fold improvement in the detection of Hg(2+). To the best of our knowledge, Au-631 not only provide the first example for detecting CH(3)Hg(+) but also have the lowest LOD value for Hg(2+) when compared to other AuNC-based Hg(2+) sensors. Importantly, this probe was successfully applied to the determination of Hg(2+) and CH(3)Hg(+) in seawater.     

淀粉-钛-硅复合物的制备表征和吸附性能

通过化学键合法制备了有机硅氧烷改性的淀粉-钛-硅复合物,并对淀粉、淀粉-钛复合物（ST）及淀粉-钛-硅复合物（STS）进行了红外光谱、扫描电镜、X射线衍射和差示扫描量热表征。表征结果说明钛氧化物及硅氧化物均参与反应,且较均匀地分散于淀粉表面,淀粉、ST和STS三者的热稳定性逐渐增加。研究了ST和STS对金属离子Hg2＋...     

Biosorption of Hg2+, Cd2+, and Zn2+ by Ca-alginate and immobilized wood-rotting fungus Funalia trogii

Funalia trogii biomass was immobilized in Ca-alginate gel beads. The live and heat inactivated immobilized forms were used for the biosorption of Hg2+, Cd2+ and Zn2+ ions by using plain Ca-alginate gel beads as a control system. The effect of pH was investigated and the maximum adsorption of metal ions on the Ca-alginate and both live and inactivated immobilized fungal preparations were observed at pH 6.0. The temperature change between 15 and 45 degrees C did not affect the biosorption capacity. The biosorption of Hg2+, Cd2+ and Zn2+ ions on the Ca-alginate beads and on both immobilized forms was studied in aqueous solutions in the concentration range of 30-600 mg/L. The metal biosorption capacities of the heat inactivated immobilized F. trogii for Hg2+, Cd2+ and Zn2+ were 403.2, 191.6, and 54.0 mg/g, respectively, while Hg2+, Cd2+ and Zn2+ biosorption capacities of the immobilized live form were 333.0, 164.8 and 42.1 mg/g, respectively. The same affinity order on a molar basis was observed for single or multi-metal ions (Hg2+ > Cd2+ > Zn2+). The Langmuir and the Freundlich type models were found to exhibit good fit to the experimental data. The experimental data were analyzed using the first-order (Langergren equations) and the second order (Ritchie equations). The experimental biosorption capacity with time is found to be best fit the second-order equations. The alginate-fungus system could be regenerated by washing with a solution of hydrochloride acid (10 mM). The percent desorption achieved was as high as 97. The biosorbents were reused in five biosorption-desorption cycles without significant loss of their initial biosorption capacity.