Analytica Chimica Acta (v.817, #C)

In this study, we developed a novel electrospray ionization (ESI) technique based on household aluminum foil (Al foil) and demonstated the desirable features and applications of this technique. Al foil can be readily cut and folded into desired configuration for effective ionization and for holding sample solution in bulk to allowing acquisition of durable ion signals. The present technique was demonstrated to be applicable in analysis of a wide variety of samples, ranging from pure chemical and biological compounds, e.g., organic compounds and proteins, to complex samples in liquid, semi-solid, and solid states, e.g., beverages, skincare cream, and herbal medicines. The inert, hydrophobic and impermeable surface of Al foil allows convenient and effective on-target extraction of solid samples and on-target sample clean-up, i.e., removal of salts and detergents from proteins and peptides, extending ESI device from usually only for sample loading and ionization to including sample processing. Moreover, Al foil is an excellent heat-conductor and highly heat-tolerant, permitting direct monitoring of thermal reactions, e.g., thermal denaturation of proteins. Overall, the present study showed that Al-foil ESI could be an economical and versatile method that allows a wide range of applications.
Keywords: Mass spectrometry; Electrospray ionization; Aluminum foil; On-target; Direct analysis;

Probabilistic peak detection for first-order chromatographic data by M. Lopatka; G. Vivó-Truyols; M.J. Sjerps (9-16).
Display OmittedWe present a novel algorithm for probabilistic peak detection in first-order chromatographic data. Unlike conventional methods that deliver a binary answer pertaining to the expected presence or absence of a chromatographic peak, our method calculates the probability of a point being affected by such a peak. The algorithm makes use of chromatographic information (i.e. the expected width of a single peak and the standard deviation of baseline noise). As prior information of the existence of a peak in a chromatographic run, we make use of the statistical overlap theory. We formulate an exhaustive set of mutually exclusive hypotheses concerning presence or absence of different peak configurations. These models are evaluated by fitting a segment of chromatographic data by least-squares. The evaluation of these competing hypotheses can be performed as a Bayesian inferential task. We outline the potential advantages of adopting this approach for peak detection and provide several examples of both improved performance and increased flexibility afforded by our approach.
Keywords: Peak detection; Bayesian statistics; Chromatography; Chemometrics;

Gold nanoparticles were labeled on the OTC molecules re-adsorbed in cavities, and then copper was deposited on the electrode by the catalysis of gold nanoparticles in copper deposition solution. The derived copper was electrochemically dissolved and the oxidative currents were recorded by DPV method.A novel method to improve the sensitivity of molecularly imprinted polymer sensors was developed. Oxytetracycline (OTC), which was selected as the template molecule, was first rebound to the imprinted cavities. Gold nanoparticles were then labeled with the amino groups of OTC molecules via electrostatic adsorption and non-covalent interactions. Copper ions were catalytically reduced by the gold nanoparticles, and copper was deposited onto the electrode. The deposited copper was electrochemically dissolved, and its oxidative currents were recorded by differential pulse voltammetry (DPV). OTC could be determined indirectly within the concentration range of 3.0 × 10−10 to 1.5 × 10−7  mol L−1 with a detection limit of 6.8 × 10−11  mol L−1.
Keywords: Molecularly imprinted polymer sensor; Catalytic copper deposition; Gold nanoparticles; Oxytetracycline; Differential pulse voltammetry;

A modified Rheodyne 7520 microsample injector was used as a new solid phase microextraction (SPME)–liquid chromatography (LC) interface. The modification was focused on the construction of a new sample rotor, which was built by gluing two sample rotors together. The new sample rotor was further reinforced with 3 pieces of stainless steel tubing. The enlarged central flow passage in the new sample rotor was used as a desorption chamber. SPME fiber desorption occurred in static mode. But all desorption solvent in the desorption chamber was injected into LC system with the interface. The analytical performance of the interface was evaluated by SPME–LC analysis of PAHs in water. At least 90% polycyclic aromatic hydrocarbons (PAHs) were desorbed from a polyacrylonitrile (PAN)/C18 bonded fuse silica fiber in 30 s. And injection was completed in 20 s. About 10–20% total carryovers were found on the fiber and in the interface. The carryover in the interface was eliminated by flushing the desorption chamber with acetonitrile at 1 mL min−1 for 2 min. The repeatability of the method was from 2% to 8%. The limit of detection (LOD) was in the mid pg mL−1 range. The linear ranges were from 0.1 to 100 ng mL−1. The new SPME–LC interface was reliable for coupling SPME with LC for both qualitative and quantitative analysis.
Keywords: Solid phase microextraction (SPME); Interface; Liquid chromatography (LC); Polycyclic aromatic hydrocarbons (PAHs);

The current article presents a mathematical description of the distribution of the enzyme reaction product around an enzyme-linked immunosorbent assay (ELISA) region of finite length created within a microfluidic channel. An analytical expression has been derived for this diffusion-reaction system relating the measured signal to the various operating parameters in the limit of slow diffusion across the assay segments. The predictions of this model have been shown to agree well with the recent experimental reports by Yanagisawa et al.[18] on such a device. The current analysis also shows that quantitating ELISAs based on measurements made in the interfacial region between two assay segments is prone to error. However, such errors can be practically eliminated if the assay signal is collected from a region where this quantity deviates from its asymptotic limit far away from the interface by less than 5%. Moreover, the mathematical analysis suggests that the axial extent of an assay region (L) in these devices may be reduced to about 3 mm before signal cross-talk with its neighboring segments begins to affect the quantitation process. The reported value for L corresponds to a sample volume requirement of 3 nL per assayed analyte in a 10 μm deep and 100 μm wide microfluidic channel, which is nearly 3 orders of magnitude smaller than that required on microarray based platforms.
Keywords: Diffusion-reaction system; ELISA; mathematical model; microfluidics; multiplex assay;

Herein, we report the development of extremely sensitive sandwich assay of kanamycin using a combination of anti-kanamycin functionalized hybrid magnetic (Fe3O4) nanoparticles (MNPs) and 2-mercaptobenzothiazole labeled Au-core@Ag-shell nanoparticles as the recognition and surface-enhanced Raman scattering (SERS) substrate, respectively. The hybrid MNPs were first prepared via surface-mediated RAFT polymerization of N-acryloyl-l-glutamic acid in the presence of 2-(butylsulfanylcarbonylthiolsulfanyl) propionic acid-modified MNPs as a RAFT agent and then biofunctionalized with anti-kanamycin, which are both specific for kanamycin and can be collected via a simple magnet. After separating kanamycin from the sample matrix, they were sandwiched with the SERS substrate. According to our experimental results, the limit of detection (LOD) was determined to be 2 pg mL−1, this value being about 3–7 times more than sensitive than the LOD of previously reported results, which can be explained by the higher SERS activity of silver coated gold nanoparticles. The analysis time took less than 10 min, including washing and optical detection steps. Furthermore, the sandwich assay was evaluated for investigating the kanamycin specificity on neomycin, gentamycin and streptomycin and detecting kanamycin in artificially contaminated milk.
Keywords: Superparamagnetic nanoparticles; Polymer brushes; Kanamycin; Surface enhanced Raman spectroscopy;

Label-free fluorescent biosensor based on the target recycling and Thioflavin T-induced quadruplex formation for short DNA species of c-erbB-2 detection by Jinghua Chen; Jia Lin; Xi Zhang; Shuxian Cai; Dongzhi Wu; Chunyan Li; Sheng Yang; Jing Zhang (42-47).
Non-invasive early diagnosis of breast cancer is the most effective way to improve the survival rate and increase more chances of breast-conserving. In this paper, we developed a label-free fluorescent biosensor based on nuclease assisted target recycling and Thioflavin T-induced quadruplex formation for short DNA species of c-erbB-2 detection in saliva. By employing the strategy, the sensor can detect as low as 20 fM target DNA with high discrimination ability even against single-base mismatch sequence. To the best of our knowledge, the proposed sensor is the first attempt to apply Thioflavin T that possesses outstanding structural selectivity for G-quadruplex in DNA amplification techniques, which may represent a promising path toward direct breast cancer detection in saliva at the point of care.
Keywords: Fluorescent biosensor; Target recycling; Thioflavin T; Quadruplex; c-erbB-2; Saliva;

Correlations between the zeta potentials of silica hydride-based stationary phases, analyte retention behaviour and their ionic interaction descriptors by Chadin Kulsing; Yuanzhong Yang; Caesar Munera; Colby Tse; Maria T. Matyska; Joseph J. Pesek; Reinhard I. Boysen; Milton T.W. Hearn (48-60).
In this study, the zeta potentials of type-B silica, bare silica hydride, the so-called Diamond Hydride™ and phenyl substituted silica hydride stationary phases have been measured in aqueous-organic media and correction procedures developed to account for the more negative zeta potential values in media containing different acetonitrile contents. Retention studies of 16 basic, acidic and neutral compounds were also performed with these four stationary phases with mobile phases containing 0.1% (v/v) formic acid and various acetonitrile–water compositions ranging from 0–90% (v/v) acetonitrile. The retention properties of these analytes were correlated to the corrected stationary phase zeta potentials measured under these different mobile phase conditions with R 2 values ranging from 0.01 to 1.00, depending on the stationary phase and analyte type. Using linear solvation energy relationships, stationary phase descriptors for each stationary phase have been developed for the different mobile phase conditions. Very high correlations of the zeta potentials with the ionic interaction descriptors were obtained for the type-B silica and the Diamond Hydride™ phases and good correlation with bare silica hydride material whilst there was no correlation observed for the phenyl substituted silica hydride phase. The nature of the retention mechanisms which gives rise to these different observations is discussed. The described methods represent a useful new approach to characterize and assess the retention properties of silica-hydride based chromatographic stationary phases of varying bonded-phase coverage and chemistries, as would be broadly applicable to other types of stationary phase used in the separation sciences.
Keywords: Hydrophilic interaction chromatography; Linear solvation energy relationship; Silica hydride; Zeta potential;