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.     

Detection of various self-assembled monolayers by AlN-based film bulk acoustic resonator

Various self-assembled monolayers such as carcinoembryonic antigen (CEA), beta actin, and bovine serum albumin (BSA) were detected using an AlN-based film bulk acoustic resonator (FBAR). AlN thin film was deposited by reactive RF magnetron sputtering, on a substrate of Mo (100 nm)/Ti (34 nm)/SiO₂ (480 nm)/Si (300 μm)/Si₃N₄ (300 nm). The film showed a strongly c-axis preferred orientation with a main (0 0 2) peak, as well as a good full width at half maximum (FWHM) of 2.50° in XRD and rocking curve results. The AlN-based FBAR was confirmed to have a resonant frequency of 2.477 GHz and a sensitivity of 3514 Hz cm²/ng. In beta actin, BSA, and CEA, the frequency properties showed variation values of 472.142, 932.573, and 685.421 kHz and mass sensitivities of 3530, 3506, and 3514 Hz-cm²/ng, respectively. The FBAR sensor was confirmed to be very useful for detecting target antigens through the binding of an antigen and an anti-body.     

Sequence Specific Label-Free DNA Sensing Using Film-Bulk-Acoustic-Resonators

A label-free biosensor (for detection of DNA sequences) based on film-bulk-acoustic-resonator (FBAR) is presented in this letter. The FBAR's resonant frequency shifts to a lower value when a complementary single-strand DNA sequence is hybridized with a DNA probe sequence on an Au-coated FBAR surface. The sensor is capable of distinguishing a complementary DNA that is mismatched to a probe DNA by a single nucleotide. The label-free, highly sensitive and selective, and real-time detection of DNA sequence could easily be made into an array for combinatory DNA sequencing, and could possibly help geneticists to detect specific DNA sequences accurately and fast, without any expensive optical scanning or imaging.     

Measuring the mass of thin films and adsorbates using magnetoelastic techniques

Magnetoelastic sensor techniques have the unique characteristics of being able to wirelessly detect resonant frequency shifts of a magnetoelastic foil in response to differences in the foil mass. However, the mathematical expression that links the resonant frequency shift with the change in the mass of the magnetoelastic foil is rarely reported. Furthermore, this relationship is not easy to ascertain due to potential changes in the Young's modulus of the sensor upon a change in mass loading. In this paper, we have shown that adsorption of water vapor from the gas phase by magnetoelastic ribbons coated with a two layer porous thin film (SiO2/Pt-TiO2) induces large changes in the effective Young's modulus of the sensor. We also demonstrated that the change in Young's modulus upon mass loading can be eliminated from the relationship between mass loading and shifts in resonant frequency by using a technique that we refer to as the two different length sensor method (TDLS). This methodology permits the conversion of the magnetoelastic sensor into a microbalance. From data presented in this paper, we illustrate that the sensitivity for the same sensor can range between 214 Hz/mg for mass loadings of Au to 438 kHz/mg for acetone. In the case of water adsorption, frequency shifts varies from 20.0 kHz/mg when Deltam 相似文献   

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.     

Fabrication and performance analysis of film bulk acoustic wave resonators

In this paper, a radio frequency reactive sputtering deposition technique for piezoelectric aluminum nitride (AlN) thin film formation on a gold (Au) bottom electrode and its successful application in a film bulk acoustic resonator (FBAR) are investigated. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements show that the AlN films were deposited onto an Au bottom electrode with highly c-axis-preferred orientation, well-textured columnar structure with a fairly uniform grain size of approximately 83 nm. The roughness is measured at a root-mean square (RMS) value of 5.4 nm and the average peak to valley of each grain column is 46.3 nm. The FBAR consists of an AlN piezoelectric thin film sandwiched between Au electrodes, all of which lie on a thin low-stress silicon nitride which serves as a support membrane on silicon. The performance of FBAR device exhibits a significant of the series quality factor (Q_s), the parallel quality factor (Q_p), the effective electromechanical coupling coefficient (k_eff²), and the bandwidths are 97, 120, 5.1%, and 24 MHz, respectively.     

Miniature high-frequency longitudinal wave mass sensors in liquid

In this paper, micromachined longitudinal wave resonant mass sensors operating near 1 GHz in a liquid environment are investigated and characterized. Mass sensitivities of the film bulk acoustic resonator (FBAR) and high-tone bulk acoustic resonator (HBAR) microbalances with small size are measured to be 782.7 cm(2)/g (50 times larger than that of conventional bulky quartz crystal microbalance) and 9.3 cm(2)/g, respectively. Based on the mass sensitivities and frequency noise floor, the minimum detectable mass of the FBAR and HBAR are estimated to be 2.8 ng/cm(2) and 11.9 ng/cm(2) in liquid, respectively.     

ZnO based film bulk acoustic resonator as infrared sensor

This paper reported the investigation of an infrared (IR) sensitive, ZnO based Film Bulk Acoustic Resonator (FBAR). The resonant frequency of the FBAR decreased under IR illumination, and results demonstrated a linear dependence on IR intensity. The sensing mechanism is attributed to the temperature-dependent Young's modulus of the resonator material (ZnO), which subsequently shifts the resonant frequency. Thickness Field Excitation FBAR and Lateral Field Excitation (LFE) FBAR were fabricated and characterized with detection limits of 0.7 μW/mm² and 2 μW/mm², respectively, but the LFE FBAR exhibited higher IR sensitivity.     

A universal sensor for mercury (Hg, Hg(I), Hg(II)) based on silver nanoparticle-embedded polymer thin film

Detection of mercury at concentration levels down to parts-per-billion is a problem of fundamental and practical interest due to the high toxicity of the metal and its role in environmental pollution. The extensive research in this area has been focused primarily on specific sensing of mercuric (Hg(2+)) ion. As mercury exists in the oxidation states, +2, +1 and 0 all of which are highly toxic, a universal sensor covering all the three while ensuring high sensitivity, selectivity, and linearity of response, and facilitating in situ as well as ex situ deployment, would be very valuable. Silver nanoparticle-embedded poly(vinyl alcohol) (Ag-PVA) thin film fabricated through a facile protocol is shown to be a fast, efficient and selective sensor for Hg(2+), Hg(2)(2+) and Hg in aqueous medium with a detection limit of 1 ppb. The sensor response is linear in the 10 ppb to 1 ppm concentration regime. A unique characteristic of the thin film based sensor is the blue shift occurring concomitantly with the decrease in the surface plasmon resonance absorption upon interaction with mercury, making the sensing highly selective. Unlike the majority of known sensors that work only in situ, the thin film sensor can be used ex situ as well. Examination of the thin film using microscopy and spectroscopy through the sensing process provides detailed insight into the sensing event.     

2.4GHz射频薄膜体声波谐振器的研制

提出了基于ZnO压电薄膜多层结构的2.4GHz射频薄膜体声波谐振器,并进行了研究.采用修正后的Mason等效电路模型对器件的谐振特性进行了分析和模拟.给出了采用MEMS工艺制备器件的工艺流程,并利用射频网络分析仪对实验器件进行了测试.利用多点数值拟合的方法消除射频测试中引入的寄生分布参数,提取出器件的实际参数:器件的串联谐振频率fs和并联谐振频率fp分别为2.3714GHz和2.3772GHz,相应的有效机电耦合系数为0.598%;串联谐振频率处和并联谐振频率处的Q值分别为500.3和425.5,f·Q值乘积达到1.2×1012.该谐振器器件的有效直径为200μm,样品实际尺寸为1.2mm×1.2mm×0.3mm,可用来制备体积小、高性能和低相噪的射频振荡器.     

Sensitive and selective detection of mercury (II) based on the aggregation of gold nanoparticles stabilized by riboflavin

Gold nanoparticles (AuNPs) can be stabilized by riboflavin against tris buffer-induced aggregation. However, in the presence of mercury (II) (Hg2+), riboflavin can be released from the AuNPs surface and the riboflavin-Hg2+ complex formed, leading to the aggregation of AuNPs in tris buffer. The aggregation extent depends on the concentration of Hg2+. Based on the aggregation extent, a simple and sensitive method of determining Hg2+ is developed. The method enables the detection of Hg2+ over the concentration range of 0.02-0.8 microM, with a detection limit (3sigma) of 14 nM, and shows excellent selectivity for Hg2+ over other metal ions (Cu2+, Co2+, Cd2+, Pb2+, Mg2+, Zn2+, Ag+, Ce3+, Ca2+, Al3+, K+). More importantly, the method avoids complicated surface modifications and tedious separation processes.     

Air gap type thin film bulk acoustic resonator fabrication using simplified process

In this study we propose a simplified process for making an air-gap-type film bulk acoustic resonator (FBAR) using the magnesium (Mg) sacrificial layer. The Mg sacrificial layer minimizes damage to other layers in the wet etching process because of its short etching time. Also the Mg sacrificial layer plays the role of etching aisle and air-gap simultaneous during the etching process. In addition, our proposed process can reduce the number of FBAR fabrication steps when compared with previous dry etching techniques. The FBAR's resonant frequency characteristics successfully show performance from 2.44 to 3.11 GHz.     

Luminescent, freestanding composite films of Au15 for specific metal ion sensing

A highly luminescent freestanding film composed of the quantum cluster, Au(15), was prepared. We studied the utility of the material for specific metal ion detection. The sensitivity of the red emission of the cluster in the composite to Cu(2+) has been used to make a freestanding metal ion sensor, similar to pH paper. The luminescence of the film was stable when exposed to several other metal ions such as Hg(2+), As(3+), and As(5+). The composite film exhibited visual sensitivity to Cu(2+) up to 1 ppm, which is below the permissible limit (1.3 ppm) in drinking water set by the U.S. environmental protection agency (EPA). The specificity of the film for Cu(2+) sensing may be due to the reduction of Cu(2+) to Cu(1+)/Cu(0) by the glutathione ligand or the Au(15) core. Extended stability of the luminescence of the film makes it useful for practical applications.     

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 mercury(II) by quantum dot/DNA/gold nanoparticle ensemble based nanosensor via nanometal surface energy transfer

An ultrasensitive fluorescent sensor based on the quantum dot/DNA/gold nanoparticle ensemble has been developed for detection of mercury(II). DNA hybridization occurs when Hg(II) ions are present in the aqueous solution containing the DNA-conjugated quantum dots (QDs) and Au nanoparticles. As a result, the QDs and the Au nanoparticles are brought into the close proximity, which enables the nanometal surface energy transfer (NSET) from the QDs to the Au nanoparticles, quenching the fluorescence emission of the QDs. This nanosensor exhibits a limit of detection of 0.4 and 1.2 ppb toward Hg(II) in the buffer solution and in the river water, respectively. The sensor also shows high selectivity toward the Hg(II) ions.     

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.     

Improved crystallization characteristics of ZnO thin film grown onto a-C:H film used as a buffer layer

We employed a-C:H buffer layer to improve the crystalline property of ZnO thin film for the membrane film bulk acoustic resonator (FBAR). The a-C:H film as a buffer layer is prepared by applying dc bias of 200 V and also this sample showed a smoother surface roughness, higher hardness and Young's modulus when compared to the other samples. In addition, the FWHM value was improved from 7.5 to 4.3° on a-C:H film. The fabricated FBAR device showed the resistivity of 0.73 × 10⁸ Ω when compared with no buffer layer and the frequency characteristics of the FBAR were finally confirmed to be 1.15 GHz and 21.24 dB, respectively.     

Characteristics of pure-shear mode BAW resonators consisting of (1120) textured ZnO films

Thickness pure-shear mode film bulk acoustic wave resonators (FBARs) made of (1120) textured ZnO films have been fabricated. We also have fabricated FBAR structure consisting of two layers of the (1120) textured ZnO film with opposite polarization directions. This FBAR structure operated in second overtone pure-shear mode and allowed shear-mode FBARs at higher frequency. The effective electromechanical coupling coefficients k2 of pure-shear mode FBAR and second overtone pure-shear mode FBAR in this study were found to be 3.3% and 0.8%, respectively. The temperature coefficient of frequency (TCF) of thickness extensional mode FBAR, pure-shear mode FBAR, and second overtone pure-shear mode FBAR were measured in the temperature range of 10-60 degrees C. TCF values of -63.1 ppm/degrees C, -34.7 ppm/degrees C, and -35.6 ppm/degrees C were found for the thickness extensional mode FBAR, the pure-shear mode FBAR, and the second overtone pure-shear mode FBAR, respectively. These results demonstrated that pure-shear mode ZnO FBARs have more stable temperature characteristics than the conventional thickness extensional mode ZnO FBARs.     

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.     

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.