High-performance liquid chromatographic assay of N(G)-monomethyl-L-arginine, N(G),N(G)-dimethyl-L-arginine, and N(G),N(G)'-dimethyl-L-arginine using 4-fluoro-7-nitro-2, 1,3-benzoxadiazole as a fluorescent reagent

N(G)-Monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (ADMA), and N(G),N(G)'-dimethyl-L-arginine (SDMA) are emerging cardiovascular risk factors. A high-performance liquid chromatographic method with fluorescence detection for the simultaneous determination of L-NMMA, ADMA and SDMA is described. The assay employed 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) as a fluorescent derivatization reagent. After solid phase extraction with cation-exchange column, the methylated arginines were converted to fluorescent derivatives with NBD-F, and the derivatives were separated within 32 min on a reversed-phase column. Nomega-Propyl-L-arginine was Used as an internal standard. Extrapolated detection limits were 12 nM (12 fmol per injection) for L-NMMA and 20 nM (20 fmol per injection) for ADMA and SDMA, respectively, with a signal-to-noise ratio of 3. The calibration curves for L-NMMA, ADMA and SDMA were linear within the range of 50-5000 fmol. The method was applied to the quantitative determination of L-NMMA, ADMA and SDMA in 200 microl of rat plasma. The concentrations of L-NMMA, ADMA and SDMA in rat plasma were 0.16 +/- 0.03, 0.80 +/- 0.25 and 0.40 +/- 0.21 microM, respectively (n = 5).     

A simple and fast liquid chromatography–tandem mass spectrometry method for measurement of underivatized <Emphasis Type="SmallCaps">l</Emphasis>-arginine,symmetric dimethylarginine,and asymmetric dimethylarginine and establishment of the reference ranges

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase and an established biomarker for endothelial function, while symmetric dimethylarginine (SDMA), an emerging biomarker for renal function, has been shown to outperform creatinine-based equations for estimated glomerular filtration rate. In order to study these analytes for clinical research, a fast and simple method for measuring arginine (ARG), SDMA, and ADMA in plasma by liquid chromatography–tandem mass spectrometry (LC-MS/MS) has been developed. Plasma (50 μL) was mixed with 50 μL of internal standard of ¹³C-arginine and d₇-ADMA followed by protein precipitation with methanol containing 1% ammonium acetate (300 μL). After centrifugation, the supernatant (100 μL) was mixed with 300 μL of acetonitrile with 1% formic acid, and the mixture was injected onto a silica column monitored by a mass spectrometer. The analytical cycle time was 5.0 min. The method was linear from 5.7 to 489.7 μM for ARG, 0.06 to 5.15 μM for SDMA, and from 0.34 to 5.65 μM for ADMA, with an accuracy of 99.0–120.0%. Total coefficients of variation for all analytes ranged from 2.7% to 7.7% for three concentration levels. The effects of hemolysis, lipemia, uremia, icterus, specimen tube types, storage at different temperature, and freeze/thaw were thoroughly investigated. Reference ranges were established using 51 well-defined reference subjects (12 men and 39 women, age 19–64 years): 53.1–129.7 μM for ARG, 0.32–0.65 μM for SDMA, and 0.36–0.67 μM for ADMA. In conclusion, the validated LC-MS/MS method described here offers a fast and reliable ARG, SDMA, and ADMA quantitation in plasma with minimum sample preparation.     

Silica nanoparticles for separation of biologically active amines by capillary electrophoresis with laser-induced native fluorescence detection

This paper describes the analysis of biologically active amines by capillary electrophoresis (CE) in conjunction with laser-induced native fluorescence detection. In order to simultaneously analyze amines and acids as well as to achieve high sensitivity, 10 mM formic acid solutions (pH < 4.0) containing silica nanoparticles (SiNPs) were chosen as the background electrolytes. With increasing SiNP concentration, the migration times for seven analytes decrease as a result of increase in electroosmotic flow (EOF) and decrease in their electrophoretic mobilities against EOF. A small EOF generated at pH 3.0 reveals adsorption of SiNPs on the deactivated capillary wall. The decreases in electrophoretic mobilities with increasing SiNP concentration up to 0.3x indicate the interactions between the analytes and the SiNPs. Having a great sensitivity (the limits of detection at a signal-to-noise ratio (S/N) = 3 of 0.09 nM for tryptamine (TA)), high efficiency, and excellent reproducibility (less than 2.4% of the migration times), this developed method has been applied to the analysis of urinal samples with the concentrations of 0.50 +/- 0.02 microM, 0.49 +/- 0.04 microM, and 74 +/- 2 microM for TA, 5-hydroxytryptamine, and tryptophan, respectively. The successful examples demonstrated in this study open up a possibility of using functional nanoparticles for the separation of different analytes by CE.     

Analysis of glyphosate and glufosinate by capillary electrophoresis-mass spectrometry utilising a sheathless microelectrospray interface

The potential of capillary electrophoresis combined with mass spectrometry for the simultaneous determination of two herbicides (glyphosate and glufosinate) and their metabolites (aminomethylphosphonic acid and methylphosphinicopropionic acid) as the native species is demonstrated utilising a simple microelectrospray interface. The interface uses the voltage applied to the CE capillary to drive separation and generate the electrospray, avoiding sample dilution associated with the use of a sheath liquid interface. The chemistry of the internal walls of the capillary has a marked influence on peak shape, and appropriate choice is essential to successful operation of the interface. A linear polyacrylamide coated capillary, which has no electroosmotic flow, gave best reproducibility, with precision of migration time and peak area in the range 1-2 and 7-12% RSD, respectively, for the four analytes. Limits of detection, low-pg on-column, are substantially better than for previous methods and calibration curves over the range 1-100 microM have R2 values greater than 0.97. The observed concentration limit of detection for glyphosate in water is 1 microM and for a water-acetone extract of wheat is 2.5 microM, allowing the underivatised herbicide to be detected at 10% of the maximum residue limit in wheat.     

高效液相色谱法测定大鼠神经组织中的硝酸盐和亚硝酸盐

 建立了大鼠神经组织中亚硝酸盐和硝酸盐的高效液相色谱测定方法,以用于研究一氧化氮在糖尿病慢性神经病变中的作用。在1 μmol/L～25 μmol/L的浓度范围内,NO2-和NO3-的峰面积与浓度的线性相关系数>0.991;最低检测浓度分别为0.2 μmol/L和0.5 μmol/L;日内、日间相对标准偏差<14%。对各实验组大鼠的初步测定结果表明,糖尿病组及糖尿病胰岛素(IGF)治疗组的NO2-和NO3-水平均低于对照组。 关键词：高效液相色谱法;一氧化氮;硝酸盐;亚硝酸盐;糖尿病神经病变     

Terpenoids with a new skeleton and novel triterpenoids with anti-inflammatory effects from Garcinia subelliptica

Three novel phloroglucinol derivatives, garcinielliptones F (1), H (3), and I (4), and two novel terpenoids, garcinielliptones G (2) and J (5), with a new skeleton have been isolated from the seeds of Garcinia subelliptica. Their structures, including relative configurations, were elucidated by spectroscopic methods and computer-generated molecular modeling. Compound 1 showed potent inhibitory effects on the release of beta-glucuronidase and lysozyme from rat neutrophils that had been stimulated with formyl-Met-Leu-Phe (fMLP)/cytochalasin B (CB). This effect was concentration-dependent with IC(50) values of 26.9+/-2.6 and 20.0+/-1.3 microM, respectively. Compound 1 also showed a potent concentration-dependent inhibitory effect on superoxide anion generation in rat neutrophils stimulated with fMLP/CB, with an IC(50) value of 17.0+/-0.9 microM. Compound 4 showed a potent inhibitory effect on NO production in culture media of N9 cells in response to lipopolysaccharide (LPS)/interferon-gamma (IFN-gamma) in a concentration-dependent manner with an IC(50) value of 7.4+/-0.2 microM.     

Bond dissociation energies and structures of CuNO(+) and Cu(NO)(2)(+)

The bond dissociation energies of CuNO(+), Cu(NO)(2)(+), and CuAr(+) are determined by means of guided ion beam mass spectrometry and quantum chemical calculations. From the experiment, the values D(0)(Cu(+)-NO) = 1.13 +/- 0.05, D(0)(ONCu(+)-NO) = 1.12 +/- 0.06, D(0)(Cu(+)-Ar) = 0.50 +/- 0.07, and D(0)(Cu(+)-Xe) = 1.02 +/- 0.06 eV are obtained. The computational approaches corroborate these results and provide additional structural data. The relative values of D(0)(Cu(+)-NO) and D(0)(Cu(+)-Xe) are consistent with the approximately thermoneutral formation of CuXe(+) upon interacting CuNO(+) with xenon. The sequential bond dissociation energies of Cu(NO)(2)(+) exhibit a trend similar to those of other Cu(I) complexes described in the literature. Although metathesis of nitric oxide to N(2) and O(2) is of considerable interest, no evidence for N-N- or O-O-bond formations in Cu(NO)(n)(+) ions (with n up to 3) is obtained within the energy range studied experimentally.     

LC-APCI-MS法同时分离测定人体血浆中的精氨酸及二甲基精氨酸的含量

建立了简单、灵敏和快速分离测定人体血浆中L-精氨酸(ARG)、不对称二甲基精氨酸(ADMA)和对称二甲基精氨酸(SDMA)的等度高效液相色谱-质谱联用方法.采用选择性离子检测(SIM)和大气压化学电离离子化(APCI),L-高精氨酸作内标,整个方法测定时间在5min以内.ARG,ADMA和SDMA的分析限均为0.2μmol/L,日间和日内测定的精密度分别为2.9%～6.7%和2.1%～5.2%,标准加入回收率为94.0%～105.0%.采用上述方法测定人体血浆中的精氨酸及二甲基精氨酸的含量,结果令人满意.     

A deconvolution method for the separation of specific versus nonspecific interactions in noncovalent protein-ligand complexes analyzed by ESI-FT-ICR mass spectrometry

A method to separate specific and nonspecific noncovalent interactions observed in ESI mass spectra between a protein and its ligands is presented. Assuming noncooperative binding, the specific ligand binding is modeled as a statistical distribution on identical binding sites. For the nonspecific fraction we assume a statistical distribution on a large number of "nonspecific" interacting sites. The model was successfully applied to the noncovalent interaction between the protein creatine kinase (CK) and its ligands adenosine diphosphate (ADP) and adenosine triphosphate (ATP) that both exhibit nonspecific binding in the mass spectrum. The two sequential dissociation constants obtained by applying our method are K(1,diss) = 11.8 +/- 1.5 microM and K(2,diss) = 48 +/- 6 microM for ADP. For ATP, the constants are K(1,diss) = 27 +/- 7 microM and K(2,diss) = 114 +/- 27 microM. All constants are in good correlation with reported literature values. The model should be valuable for systems with a large dissociation constant that require high ligand concentrations and thus have increased potential of forming nonspecific adducts.     

Probing heme coordination states of inducible nitric oxide synthase with a ReI(imidazole-alkyl-nitroarginine) sensitizer-wire

Mammalian inducible nitric oxide synthase (iNOS) catalyzes the production of l-citrulline and nitric oxide (NO) from L-arginine and O2. The Soret peak in the spectrum of the iNOS heme domain (iNOSoxy) shifts from 423 to 390 nm upon addition of a sensitizer-wire, [ReI-imidazole-(CH2)8-nitroarginine]+, or [ReC8argNO2]+, owing to partial displacement of the water ligand in the active site. From analysis of competitive binding experiments with imidazole, the dissociation constant (Kd) for [ReC8argNO2]+-iNOSoxy was determined to be 3.0+/-0.1 microM, confirming that the sensitizer-wire binds with higher affinity than both L-arginine (Kd=22+/-5 microM) and imidazole (Kd=14+/-3 microM). Laser excitation (355 nm) of [ReC8argNO2]+-iNOSoxy triggers electron transfer to the active site of the enzyme, producing a ferroheme in less than approximately 1 micros.     

Method development for the analysis of particle phase substituted methoxy phenols and aromatic acids from biomass burning using capillary electrophoresis/electrospray ionization mass spectrometry (CE/ESI-MS)

A method is developed for the determination of substituted methoxy phenols and aromatic acids in biomass burning aerosol using capillary electrophoresis (CE) coupled to an electrospray ionization mass spectrometer. Background electrolytes (BGEs) containing ammonium acetate, ammonium hydroxide and 10% (v/v) methanol at pH 9.1 and ammonium hydroxide at pH 11 are investigated for their suitability. A good linearity is found for all analytes in the range of 1-50 microM for the ammonium acetate based BGE and 1-40 microM for the ammonium hydroxide BGE. The detection limit ranged from 0.1 to 1.0 microM for the ammonium acetate based BGE and 0.3 to 0.7 microM for the ammonium hydroxide BGE. The relative standard deviation (R.S.D.) is typically less than 0.5% (ammonium acetate based BGE) and 4.2% (ammonium hydroxide BGE) for the migration time and 3-9% (ammonium acetate based BGE) and 2.5-8% (ammonium hydroxide BGE) for the peak area (n = 5). The analytical time was less than 10 min for both methods. The proposed methods are fast, sensitive and quantitative and can be applied to the analysis of complex biomass burning aerosol samples without complex pre-treatment. The results from the analysis of real biomass burning samples demonstrate the suitability of the proposed methods to the analysis of low concentration water soluble organic carbon (WSOC) in biomass burning samples. The fast analytical time and high sensitivity of the proposed methods enables the analysis of a large number of size segregated impactor samples from biomass burning aerosols.     

A simple micellar electrokinetic capillary chromatographic method for the quantitative analysis of organic expectorants

A simple and rapid micellar electrokinetic capillary chromatographic method is described for the separation and quantification of five expectorant drugs, including ambroxol (AMB), bromhexine (BRM), carbocysteine, guaiacol and guaifenesin. The drugs were separated in a mixed solution of phosphate buffer (35 mM; pH 3.90) and acetonitrile (75:25, v/v) with sodium dodecylsulfate (120 mM) as the micellar source, and the separated drugs were directly monitored with UV detector (200 nm). Several key parameters affecting the separation and analysis of the drugs were studied and optimized. Based on the corrected peak-area ratios of the drugs to an internal standard (7-hydroxy-4-methyl-coumarin) versus the concentration of the drugs, the established method is applicable to quantify AMB and BRM each over 20-150 microM, carbocysteine over 100-1500 microM, guaiacol and guaifenesin each over 10-150 microM. The detection limits (S/N=3; 0.5 psi, 5 s injection) of the method for the analytes are in the range of 3.0-5.0 microM (except that of carbocysteine at 30 microM). The precision (relative standard deviation) and accuracy (relative error) of the method for the intra-day (n=3) and inter-day (n=5) analyses of the analytes at three levels are all below 4%. The method is speedy with a run time of about 6 min for the analysis of the five analytes. Application of this method to the analysis of AMB and BRM in pharmaceutical preparations or AMB in the urine of a dosed subject proved simple and effective.     

Post-capillary reaction detection in capillary electrophoresis based on the streptavidin-biotin interaction. Optimization and application to single cell analysis.

A class-selective post-capillary reaction detection method for capillary electrophoresis is described in which a streptavidin-fluorescein isothiocyanate (streptavidin-FITC) conjugate is used to detect biotin moieties. The selective binding of biotin moieties to the streptavidin-FITC conjugate causes an enhancement of fluorescence proportional to the concentration of biotin present. After capillary electrophoresis the separated analytes react with streptavidin-FITC in a coaxial reactor and are then detected either by a benchtop spectrofluorometer (2.5 microM detection limit) or by an epi-fluorescence microscope (1 x 10(-7) M detection limit). The method is used to examine biotinylated species in a crude mammalian cell lysate which was found to contain 83+/-3 fmol in 3600 cell volumes. In addition, it is used to examine the uptake of biotin by individual sea urchin oocytes. The results indicate that, in the oocytes, biocytin is the prevalent form of biotin and its concentration varies widely between cells (mean=2+/-2 microM).     

Determination of methylated arginines by column-switching high-performance liquid chromatography-fluorescence detection

A column-switching high-performance liquid chromatography (HPLC)-fluorescence detection method for the determination of three methylated arginines, N(G)-monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (asymmetric dimethyl-L-arginine, ADMA), and N(G),N(G)'-dimethyl-L-arginine (symmetric dimethyl-L-arginine, SDMA), which are endogenous nitric oxide synthase inhibitors, was developed. After fluorescence derivatization of plasma samples with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), the samples were injected into the HPLC system. The NBD-derivatized methylated arginines were trapped on a cation exchange column with filter to remove proteins, separated within 42 min on a reversed-phase column, and detected at an emission wavelength of 530 nm with excitation at 470 nm. The detection limits were 10 fmol for L-NMMA and 20 fmol for ADMA and SDMA with a signal-to-noise ratio of 3. A good linearity for calibration curves for each methylated arginine was observed within the range of 50-5000 fmol using homoarginine as an internal standard. The proposed method was applied to the quantitative determination of L-NMMA, ADMA and SDMA in rat plasma. The concentrations of L-NMMA, ADMA and SDMA in rat plasma were 0.16 +/- 0.01, 0.73 +/- 0.02 and 0.41 +/- 0.05 micromol l(-1), respectively (n= 5).     

High-throughput CZE-UV determination of arginine and dimethylated arginines in human plasma

Experimental studies document that increased asymmetric dimethylarginine (ADMA) blood levels inhibit NOS significantly, reducing NO generation. ADMA measurement often needs sample cleanup by SPE prior to chromatography and precolumn derivatization that cannot be easily employed in a routine clinical setting. We set up a new reliable CE method to measure ADMA, symmetric dimethylarginine (SDMA), and arginine without sample extraction or precolumn derivatization in order to examine their concentrations in human plasma. Sample was concentrated prior to CE injection and analytes were monitored by UV detection. CE analysis was performed in an uncoated fused-silica capillary, 75 microm id and 60.2 cm length (50 cm to the detection window), injecting 1 s water plug (0.5 psi) followed by 10 s of the sample (0.5 psi). Separation was carried out in a 50 mmol/L Tris-phosphate run buffer at pH 2.30, 15 degrees C and 15 kV (75 microA) at normal polarity. Recovery of plasma ADMA was 101-104% and inter-day CV was less than 3%. Assay performance was evaluated measuring the levels of arginine and its dimethyl derivatives in 77 subjects. Passing-Bablok regression and Bland-Altman test for methods comparison suggest that the data obtained by our method and by a reference CE-LIF assay are similar.     

Simultaneous analysis of nitrate and nitrite in a microfluidic device with a Cu-complex-modified electrode

A CE microsystem coupled with a microchip and a copper-(3-mercaptopropyl) trimethoxysilane (Cu-MPS) complex-modified carbon paste electrode (CPE) was developed for the simultaneous analysis of nitrite and nitrate. The method is based on the electrocatalytic reduction of both analytes with the modified electrode. The Cu-MPS complex was characterized by voltammetric, XPS, and FT-IR analyses. Experimental parameters affecting the sensitivity of the modified electrode were assessed and optimized. The best separation was achieved in a 60 mm separation channel filled with a 20 mM acetate buffer of pH 5.0 containing 3.0 mM CTAB at separation field strength of -250 V/cm within 90 s. The detection potential for the simultaneous analysis of nitrite and nitrate was found to be -225 mV versus Ag/AgCl. A reproducible response (RSD of 3.2% (nitrite) and 2.8% (nitrate), n = 8) for repetitive sample injections reflected the negligible electrode fouling at the modified CPE. The interference effect was examined for other inorganic ions and biological compounds. A wide hydrodynamic range between 0.25 and 120 microM was observed for analyzing nitrite and nitrate with the sensitivities of 0.069 +/- 0.003 and 0.065 +/- 0.002 nA/microM, and the detection limits, based on S/N = 3, were found to be 0.09 +/- 0.007 and 0.08 +/- 0.009 microM, respectively. The applicability of the method to water and urine samples analyses was demonstrated.     

凝胶渗透色谱净化-超高效液相色谱-串联质谱法测定皮革制品中7种尼泊金酯类防腐剂

利用超高效液相色谱-串联质谱(UPLC-MS/MS)结合凝胶渗透色谱(GPC)技术,建立了一种快速分离和测定皮革制品中7种尼泊金酯类防腐剂的分析方法。样品经超声提取、浓缩、GPC净化,甲醇-水溶液(1:1, v/v)溶解,采用Acquity UPLCBEH C18柱(50 mm×2.1 mm, 1.7 μm)分离,以甲醇和水为流动相,梯度洗脱,电喷雾负离子模式电离,采用多反应监测模式检测和外标法定量。该方法在0.1～1.0 mg/L范围内线性关系良好(r＞0.99);在添加量为0.5～3.0 mg/kg时,平均回收率为(79.44±5.67)%～(98.07±9.50)%,相对标准偏差(RSD)为4.24%～14.00%;方法的检出限(LOD)为4～12 μg/kg,定量限(LOQ)为13.2～39.6 μg/kg。该方法操作简便、快捷、灵敏、准确,适合皮革中多种尼泊金酯类防腐剂的确证和定量测定。     

Determination of the active and inactive metabolites of prasugrel in human plasma by liquid chromatography/tandem mass spectrometry

Two fast and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS)-based bioanalytical assays were developed and validated to quantify the active and three inactive metabolites of prasugrel. Prasugrel is a novel thienopyridine prodrug that is metabolized to the pharmacologically active metabolite in addition to three inactive metabolites, which directly relate to the formation and elimination of the active metabolite. After extraction and separation, the analytes were detected and quantified using a triple quadrupole mass spectrometer using positive electrospray ionization. The validated concentration range for the inactive metabolites assay was from 1 to 500 ng/mL for each of the three analytes. Additionally, a 5x dilution factor was validated. The interday accuracy ranged from -10.5% to 12.5% and the precision ranged from 2.4% to 6.6% for all three analytes. All results showed accuracy and precision within +/-20% at the lower limit of quantification and +/-15% at other levels. The validated concentration range for the active metabolite assay was from 0.5 to 250 ng/mL. Additionally, a 10x dilution factor was validated. The interbatch accuracy ranged from -7.00% to 5.98%, while the precision ranged from 0.98% to 3.39%. Derivatization of the active metabolite in blood with 2-bromo-3'-methoxyacetophenone immediately after collection was essential to ensure the stability of the metabolite during sample processing and storage. These methods have been applied to determine the concentrations of the active and inactive metabolites of prasugrel in human plasma.     

Gas-phase basicity of methionine

Proton affinity and protonation entropy of methionine (Met) were determined by the extended kinetic method from ESI-Q-TOF tandem mass spectrometry experiments. The values, PA(Met) = 937.5 +/- 2.9 kJ mol(-1) and Delta(p)S degrees (Met) = - 22 +/- 5 J mol(-1) K(-1), lead to gas-phase basicity GB(Met) = 898.2 +/- 3.2 kJ.mol(-1). Quantum chemical calculations using density functional theory confirm that the proton affinity of Met is indeed in the 940 kJ mol(-1) range and that a significant entropy loss, of at least - 25 J mol(-1) K(-1), occurs upon protonation. This last point is evidenced here for the first time and suggests revision of the tabulated protonation thermochemistry of Met. A comparison with previous experimental data allows us to propose the following evaluated thermochemical values: PA(Met) = 943 +/- 4 kJ mol(-1) and Delta(p)S degrees (Met) = - 35 +/- 15 J mol(-1) K(-1) and GB(Met) = 900 +/- 2 kJ mol(-1).     

Monitoring of the self-assembled monolayer of 1-hexadecanethiol on a gold surface at nanomolar concentration using a piezo-excited millimeter-sized cantilever sensor

In this paper, we describe a new method of measuring alkanethiol monolayer formation on a gold surface. A gold-coated millimeter-sized rectangular-shaped lead zirconate titanate (PZT) cantilever of dimensions 3.5 x 2 x 0.05 mm, previously shown to detect a picogram level of mass change, was used to measure the adsorption kinetics of 1-hexadecanethiol in ethanol over six orders of concentration range (1 nM to 10 mM) in real time. The flexural mode of cantilever vibration, 45.5 +/- 0.01 kHz, was monitored during the self-assembly. The total resonant frequency change obtained for the 1 nM, 10 nM, 100 nM, 1 microM, 4 mM, 8 mM, and 10 mM thiol concentrations were 116 +/- 2 (n = 2), 225 (n = 1), 270 +/- 10 (n = 2), 440 +/- 10 (n = 2), 900 +/- 10 (n = 2), 900 +/- 10 (n = 2), and 900 +/- 10 (n = 2) Hz, respectively. These results compare favorably to literature results in that the rate of the monolayer formation is concentration-dependent and the exponential change during adsorption follows the reversible first-order Langmuir kinetic model. The rate constants of adsorption and desorption were 0.061 M(-1) s(-1) and 3.61 x 10(-4) s(-1), respectively. The significance of the results is that millimeter-sized PZT cantilevers can be used in real-time for characterizing self-assembly of monolayer formation at nanomolar concentration levels. In addition, at 1 nM, the adsorption was found not to be diffusion limited.