Chinese normotensive and essential hypertensive reference intervals for plasma aldosterone and renin activity by liquid chromatography-tandem mass spectrometry.

OBJECTIVES: The renin-angiotensin-aldosterone system (RAAS) regulates blood pressure. Plasma renin activities (PRA) and plasma aldosterone concentrations (PAC) are biomarkers related to RAAS. Liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based measurements for PRA and PAC have become popular. Method-specific reference intervals (RIs) are required. METHODS: Routine PRA and PAC services in a Hong Kong teaching hospital were based on LC-MS/MS methods. PRA and PAC RIs were developed for normotensive subjects and essential hypertensive (EH) patients. Healthy volunteers were recruited to establish normotensive RIs. PRA and PAC results of hypertensive patients with urine aldosterone tests for primary aldosteronism (PA) screening were retrieved from the laboratory information system. Patients without PA were included. Patients with secondary hypertension and patients on medications affecting the RAAS were excluded. The central 95% RIs were established based on the recommendations of the Clinical and Laboratory Standards Institute guideline C28-A3. RESULTS: PRA and PAC of 170 normotensive volunteers and 362 EH patients were analysed. There was no sex-specific difference in PRA and PAC for normotensive and EH reference subjects. Differences for PRA and PAC were noted between normotensive subjects aged below 45 and their older counterparts. However, such a difference was only identified for PRA but not PAC in EH patients. Age-specific RIs were established accordingly. CONCLUSIONS: This study presented age-specific LC-MS/MS RIs of PRA and PAC for both normotensive and EH populations for local Chinese in Hong Kong.

Application of Plasma-Printed Paper-Based SERS Substrate for Cocaine Detection.

Surface-enhanced Raman spectroscopy (SERS) technology is an attractive method for the prompt and accurate on-site screening of illicit drugs. As portable Raman systems are available for on-site screening, the readiness of SERS technology for sensing applications is predominantly dependent on the accuracy, stability and cost-effectiveness of the SERS strip. An atmospheric-pressure plasma-assisted chemical deposition process that can deposit an even distribution of nanogold particles in a one-step process has been developed. The process was used to print a nanogold film on a paper-based substrate using a HAuCl4 solution precursor. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the gold has been fully reduced and that subsequent plasma post-treatment decreases the carbon content of the film. Results for cocaine detection using this substrate were compared with two commercial SERS substrates, one based on nanogold on paper and the currently available best commercial SERS substrate based on an Ag pillar structure. A larger number of bands associated with cocaine was detected using the plasma-printed substrate than the commercial substrates across a range of cocaine concentrations from 1 to 5000 ng/mL. A detection limit as low as 1 ng/mL cocaine with high spatial uniformity was demonstrated with the plasma-printed substrate. It is shown that the plasma-printed substrate can be produced at a much lower cost than the price of the commercial substrate.

Nanozymes for Environmental Pollutant Monitoring and Remediation.

Nanozymes are advanced nanomaterials which mimic natural enzymes by exhibiting enzyme-like properties. As nanozymes offer better structural stability over their respective natural enzymes, they are ideal candidates for real-time and/or remote environmental pollutant monitoring and remediation. In this review, we classify nanozymes into four types depending on their enzyme-mimicking behaviour (active metal centre mimic, functional mimic, nanocomposite or 3D structural mimic) and offer mechanistic insights into the nature of their catalytic activity. Following this, we discuss the current environmental translation of nanozymes into a powerful sensing or remediation tool through inventive nano-architectural design of nanozymes and their transduction methodologies. Here, we focus on recent developments in nanozymes for the detection of heavy metal ions, pesticides and other organic pollutants, emphasising optical methods and a few electrochemical techniques. Strategies to remediate persistent organic pollutants such as pesticides, phenols, antibiotics and textile dyes are included. We conclude with a discussion on the practical deployment of these nanozymes in terms of their effectiveness, reusability, real-time in-field application, commercial production and regulatory considerations.

Strong enhancement of gold nanoparticle chemiresistor response to low-partitioning organic analytes induced by pre-exposure to high partitioning organics.

Exposing a thiol-functionalised gold nanoparticle film chemiresistor to methanol in aqueous solution results in only a small electric current response as the thiol ligand/water partition coefficient of methanol is small, leading to only minor swelling of the chemiresistor film. Nevertheless, the current response to methanol can be enhanced if the chemiresistor becomes pre-exposed to a molecule with a large ligand/water partition coefficient P (e.g. octane with Po = 104.3). The large response enhancement is achieved because methanol, when added to an aqueous solution of octane, lowers the large initial partition coefficient of octane. Octane exiting the thiol ligands then leads to strong film shrinkage resulting in a relative current change much greater than the one otherwise induced by methanol alone. This was theoretically modelled for octane and heptane (Ph = 103.6). A strong response enhancement to methanol (>20 times) was observed experimentally by exposure to 2 ppm octane compared to direct testing of methanol in aqueous solution. Besides octane and heptane, molecules with P > 107 (e.g. permethrin) can theoretically be used to provide enhancement factors of several orders of magnitude. For practical reasons, heptane and octane saturate more quickly, thus enabling more rapid detection of methanol than higher P organic molecules.

Toward Paper-Based Sensors: Turning Electrical Signals into an Optical Readout System.

Paper-based sensors are gaining increasing attention for their potential applications in resource-limited settings and for point-of-care analysis. However, chemical analysis of paper-based electronic sensors is frequently interpreted using complex software and electronic displays which compromise the advantages of using paper. In this work, we present two semiquantitative paper-based readout systems that can visually measure a change in resistance of a resistive-based sensor. The readout systems use electrochromic Prussian blue/polyaniline as an electrochromic indicator on a resistive gold nanoparticle film that is fabricated on paper. When the readout system is integrated with a resistive sensor in an electrical circuit, and a voltage is applied, the voltage drop along the readout system varies depending on the sensor's resistance. Due to the voltage gradient formed along the gold nanoparticle film, the overlaying Prussian blue/polyaniline will change color at voltages greater than its reduction voltage (green/blue for oxidized state and transparent for reduced state). Thus, the changes in resistances of a sensor can be semiquantified through color visualization by either measuring the length of the transparent film (analog readout system) or by counting the number of transparent segments (digital readout system). The work presented herein can potentially serve as an alternative paper-based display system for resistive sensors in instances where cost and weight is a premium.

High-throughput fabrication and screening improves gold nanoparticle chemiresistor sensor performance.

Chemiresistor sensor arrays are a promising technology to replace current laboratory-based analysis instrumentation, with the advantage of facile integration into portable, low-cost devices for in-field use. To increase the performance of chemiresistor sensor arrays a high-throughput fabrication and screening methodology was developed to assess different organothiol-functionalized gold nanoparticle chemiresistors. This high-throughput fabrication and testing methodology was implemented to screen a library consisting of 132 different organothiol compounds as capping agents for functionalized gold nanoparticle chemiresistor sensors. The methodology utilized an automated liquid handling workstation for the in situ functionalization of gold nanoparticle films and subsequent automated analyte testing of sensor arrays using a flow-injection analysis system. To test the methodology we focused on the discrimination and quantitation of benzene, toluene, ethylbenzene, p-xylene, and naphthalene (BTEXN) mixtures in water at low microgram per liter concentration levels. The high-throughput methodology identified a sensor array configuration consisting of a subset of organothiol-functionalized chemiresistors which in combination with random forests analysis was able to predict individual analyte concentrations with overall root-mean-square errors ranging between 8-17 µg/L for mixtures of BTEXN in water at the 100 µg/L concentration. The ability to use a simple sensor array system to quantitate BTEXN mixtures in water at the low µg/L concentration range has direct and significant implications to future environmental monitoring and reporting strategies. In addition, these results demonstrate the advantages of high-throughput screening to improve the performance of gold nanoparticle based chemiresistors for both new and existing applications.

Association of Neisseria gonorrhoeae Opa(CEA) with dendritic cells suppresses their ability to elicit an HIV-1-specific T cell memory response.

Infection with Neisseria gonorrhoeae (N. gonorrhoeae) can trigger an intense local inflammatory response at the site of infection, yet there is little specific immune response or development of immune memory. Gonococcal surface epitopes are known to undergo antigenic variation; however, this is unlikely to explain the weak immune response to infection since individuals can be re-infected by the same serotype. Previous studies have demonstrated that the colony opacity-associated (Opa) proteins on the N. gonorrhoeae surface can bind human carcinoembryonic antigen-related cellular adhesion molecule 1 (CEACAM1) on CD4⁺ T cells to suppress T cell activation and proliferation. Interesting in this regard, N. gonorrhoeae infection is associated with impaired HIV-1 (human immunodeficiency virus type 1)-specific cytotoxic T-lymphocyte (CTL) responses and with transient increases in plasma viremia in HIV-1-infected patients, suggesting that N. gonorrhoeae may also subvert immune responses to co-pathogens. Since dendritic cells (DCs) are professional antigen presenting cells (APCs) that play a key role in the induction of an adaptive immune response, we investigated the effects of N. gonorrhoeae Opa proteins on human DC activation and function. While morphological changes reminiscent of DC maturation were evident upon N. gonorrhoeae infection, we observed a marked downregulation of DC maturation marker CD83 when the gonococci expressing CEACAM1-specific Opa(CEA), but not other Opa variants. Consistent with a gonococcal-induced defect in maturation, Opa(CEA) binding to CEACAM1 reduced the DCs' capacity to stimulate an allogeneic T cell proliferative response. Moreover, Opa(CEA)-expressing N. gonorrhoeae showed the potential to impair DC-dependent development of specific adaptive immunity, since infection with Opa(CEA)-positive gonococci suppressed the ability of DCs to stimulate HIV-1-specific memory CTL responses. These results reveal a novel mechanism to explain why infection of N. gonorrhoeae fails to trigger an effective specific immune response or develop immune memory, and may affect the potent synergy between gonorrhea and HIV-1 infection.

Recent advances in paper-based sensors.

Paper-based sensors are a new alternative technology for fabricating simple, low-cost, portable and disposable analytical devices for many application areas including clinical diagnosis, food quality control and environmental monitoring. The unique properties of paper which allow passive liquid transport and compatibility with chemicals/biochemicals are the main advantages of using paper as a sensing platform. Depending on the main goal to be achieved in paper-based sensors, the fabrication methods and the analysis techniques can be tuned to fulfill the needs of the end-user. Current paper-based sensors are focused on microfluidic delivery of solution to the detection site whereas more advanced designs involve complex 3-D geometries based on the same microfluidic principles. Although paper-based sensors are very promising, they still suffer from certain limitations such as accuracy and sensitivity. However, it is anticipated that in the future, with advances in fabrication and analytical techniques, that there will be more new and innovative developments in paper-based sensors. These sensors could better meet the current objectives of a viable low-cost and portable device in addition to offering high sensitivity and selectivity, and multiple analyte discrimination. This paper is a review of recent advances in paper-based sensors and covers the following topics: existing fabrication techniques, analytical methods and application areas. Finally, the present challenges and future outlooks are discussed.

Gold nanoparticle chemiresistors operating in biological fluids.

Functionalised gold nanoparticle (Au(NP)) chemiresistors are investigated for direct sensing of small organic molecules in biological fluids. The principle reason that Au(NP) chemiresistors, and many other sensing devices, have limited operation in biological fluids is due to protein and lipid fouling deactivating the sensing mechanism. In order to extend the capability of such chemiresistor sensors to operate directly in biofluids, it is essential to minimise undesirable matrix effects due to protein and lipidic components. Ultrafiltration membranes were investigated as semi-permeable size-selective barriers to prevent large biomolecule interactions with Au(NP) chemiresistors operating in protein-loaded biofluids. All of the ultrafiltration membranes protected the Au(NP) chemiresistors from fouling by the globular biomolecules, with the 10 kDa molecular weight cut-off size being optimum for operation in biofluids. Titrations of toluene in different protein-loaded fluids indicated that small molecule detection was possible. A sensor array consisting of six different thiolate-functionalised Au(NP) chemiresistors protected with a size-selective ultrafiltration membrane successfully identified, and discriminated the spoilage of pasteurised bovine milk. This proof-of-principle study demonstrates the on-chip protein separation and small metabolite detection capability, illustrating the potential for this technology in the field of microbial metabolomics. Overall, these results demonstrate that a sensor array can be protected from protein fouling with the use of a membrane, significantly increasing the possible application areas of Au(NP) chemiresistors ranging from the food industry to health services.

Dynamic response of gold nanoparticle chemiresistors to organic analytes in aqueous solution.

We investigate the response dynamics of 1-hexanethiol-functionalized gold nanoparticle chemiresistors exposed to the analyte octane in aqueous solution. The dynamic response is studied as a function of the analyte-water flow velocity, the thickness of the gold nanoparticle film and the analyte concentration. A theoretical model for analyte limited mass-transport is used to model the analyte diffusion into the film, the partitioning of the analyte into the 1-hexanethiol capping layers and the subsequent swelling of the film. The degree of swelling is then used to calculate the increase of the electron tunnel resistance between adjacent nanoparticles which determines the resistance change of the film. In particular, the effect of the nonlinear relationship between resistance and swelling on the dynamic response is investigated at high analyte concentration. Good agreement between experiment and the theoretical model is achieved.

Gold nanoparticle chemiresistor sensor array that differentiates between hydrocarbon fuels dissolved in artificial seawater.

Gold nanoparticle films (Au(NPF)) functionalized with a range of hydrophobic and hydrophilic thiols were assembled in chemiresistor sensor arrays that were used to differentiate between complex mixtures of analytes in the aqueous phase. A chemiresistor array sampled a simple system of linear alcohols (methanol, ethanol, propan-1-ol, and butan-1-ol) dissolved in water over a range of concentrations. Discriminant analysis confirmed that the response patterns of the array could be used to successfully distinguish between the different alcohol solutions at concentrations above 20 mM for all of the alcohols except methanol, which was distinguished at concentrations above 200 mM. Alcohol solutions more dilute than these concentrations had response patterns that were not consistently recognizable and failed cross validation testing. This defined the approximate limit of discrimination for the system, which was close to the limits of detection for the majority of the individual sensors. Another Au(NPF) chemiresistor array was exposed to, and successfully identified crude oil, diesel, and three varieties of gasoline dissolved in artificial seawater at a fixed concentration. This work is a demonstration that the pattern of responses from an array of differently functionalized Au(NPF) sensors can be used to distinguish analytes in the aqueous phase.

Anthrax lethal toxin promotes dephosphorylation of TTP and formation of processing bodies.

Anthrax lethal toxin (LeTx) is composed of protective antigen (PA) and lethal factor (LF) - PA is the receptor-binding moiety and LF is a protease that cleaves mitogen-activated protein kinase kinases (MAPKKs). LeTx subverts the immune response to Bacillus anthracis in several ways, such as downregulating interleukin-8 (IL-8) by increasing the rate of IL-8 mRNA degradation. Many transcripts are regulated through cis-acting elements that bind proteins that either impede or promote degradation. Some of these RNA-binding proteins are regulated by MAPKs and previous work has demonstrated that interfering with MAPK signalling decreases the half-life of IL-8 mRNA. Here, we have localized a segment within the IL-8 3' untranslated region responsible for LeTx-induced transcript destabilization and show that this is caused by inhibition of the p38, ERK and JNK pathways. TTP, an RNA-binding protein involved in IL-8 mRNA decay, became hypophosphorylated in LeTx-treated cells and knock-down of TTP prevented LeTx from destabilizing the IL-8 transcript. Cells that were treated with LeTx exhibited increased localization of TTP to Processing bodies, which are structures that accumulate transcripts targeted for degradation. We furthermore observed that LeTx promoted the formation of Processing bodies, revealing a link between the toxin and a major mRNA decay pathway.

Inkjet-printed gold nanoparticle chemiresistors: influence of film morphology and ionic strength on the detection of organics dissolved in aqueous solution.

The influence of film morphology on the performance of inkjet-printed gold nanoparticle chemiresistors has been investigated. Nanoparticles deposited from a single-solvent system resulted in a "coffee ring"-like structure with most of the materials deposited at the edge. It was shown that the uniformity of the film could be improved if the nanoparticles were deposited from a mixture of solvents comprising N-methyl-2-pyrrolidone and water. Electrical conductivity measurements showed that both "coffee ring" and "flat" films were qualitatively similar suggesting that the films have similar nanoscale structures. To form the functional chemiresistor device, the 4-(dimethylamino)pyridine coating on the nanoparticle was exchanged with 1-hexanethiol to provide a hydrophobic sensing layer. The performance of 1-hexanethiol coated gold nanoparticle chemiresistors to small organic molecules, toluene, dichloromethane and ethanol dissolved in 1 M KCl in regard to changes in impedance and response times was unaffected by the film morphology. For larger hydrocarbons such as octane, the rate of uptake of the analyte into the film was significantly faster when the flatter nanoparticle film was used as opposed to the "coffee ring" film which has a thicker edge. Furthermore, the presence of potassium and chloride ions in the solution media does not significantly affect the impedance of the nanoparticle film at 1 Hz (<2% variation in film impedance over more than four orders of magnitude change in ionic strength). However, the ionic strength of the media affected the partitioning of the analyte into the hydrophobic nanoparticle film. The response of the sensor was found to increase with an increased salt concentration due to a salting-out of the analyte from the solution.

The cytoplasmic domain of anthrax toxin receptor 1 affects binding of the protective antigen.

The protective antigen (PA) component of anthrax toxin binds the I domain of the receptor ANTXR1. Integrin I domains convert between open and closed conformations that bind ligand with high and low affinities, respectively; this process is regulated by signaling from the cytoplasmic domains. To assess whether intracellular signals might influence the interaction between ANTXR1 and PA, we compared two splice variants of ANTXR1 that differ only in their cytoplasmic domains. We found that cells expressing ANTXR1 splice variant 1 (ANTXR1-sv1) bound markedly less PA than did cells expressing a similar level of the shorter splice variant ANTXR1-sv2. ANTXR1-sv1 but not ANTXR1-sv2 associated with the actin cytoskeleton, although disruption of the cytoskeleton did not affect binding of ANTXR-sv1 to PA. Introduction of a cytoplasmic domain missense mutation found in the related receptor ANTXR2 in a patient with juvenile hyaline fibromatosis impaired actin association and increased binding of PA to ANTXR1-sv1. These results suggest that ANTXR1 has two affinity states that may be modulated by cytoplasmic signals.

Multi-analyte sensing: a chemometrics approach to understanding the merits of electrode arrays versus single electrodes.

A peptide-modified electrode array with a different peptide on each electrode is compared with a single electrode modified with many peptides for the voltammetric measurement of concentrations of Cu(2+), Cd(2+) and Pb(2+) in solution. The single gold electrode was modified simultaneously with peptides Gly-Gly-His, glutathione and angiotensin I each coupled to thioctic acid, and thioctic acid itself, and the calibration of mixtures of ions was compared with previously published data from an array of four sensors each with an individual modification. Calibration at the multi-peptide single-electrode sensor was by two-way partial least squares (voltammetric current measured with variables 'sample' x 'potential') and for the electrode array by three-way NPLS1 ('sample' x 'potential' x 'electrode'). The advantage of designing experiments to yield multi-way data is demonstrated and discussed.

Gold nanoparticle chemiresistor sensors: direct sensing of organics in aqueous electrolyte solution.

A novel chemiresistor sensor for detection of organic analytes in high-conductivity aqueous electrolyte solution is reported. The chemiresistor sensor is based on thin films of gold nanoparticles capped with a 1-hexanethiol monolayer that is inkjet printed onto a microelectrode. In order for a change in nanoparticle film resistance to be measured, the electronic conduction must preferentially occur through the nanoparticle film rather than through the high-conductivity electrolyte solution. This was achieved by miniaturizing the chemiresistor device such that the double layer capacitance of the electrodes in contact with the electrolyte solution gives rise to a significantly larger impedance compared to the nanoparticle film resistance. This system was shown to be sensitive to simple organics dissolved in an aqueous electrolyte solution. The organic analytes, dissolved in the aqueous solution, partition into the hydrophobic nanoparticle film causing the nanoparticle film to swell, resulting in an increase in the low-frequency impedance of the sensor. An increase in the impedance, at 1 Hz, of the gold nanoparticle chemiresistor on exposure to toluene, dichloromethane, and ethanol dissolved in 1 M KCl solution was demonstrated with detection limits of 0.1, 10, and 3000 ppm, respectively. Titration curves over 3 orders of magnitude could be obtained for analytes such as toluene.

Extending the dynamic range of electrochemical sensors using multiple modified electrodes.

Multiple electrodes, combined with a chemometric strategy to calibrate the measurement response, have been used for the determination of an analyte across a broader dynamic range than is possible with a single electrode. The model system used for the detection of copper comprised electrodes modified with a self-assembled monolayer. The electrodes were modified with the copper-complexing species (3-mercaptopropionic acid, thioctic acid, and the peptides cysteine and Gly-Gly-His) and copper was determined over concentrations ranging from nanomolar to millimolar using voltammetric analysis. We have demonstrated that by combining the calibration functions from the four electrodes a better estimate (i.e. with smaller variance) of the concentration of the analyte is obtained. Measurement uncertainty is expressed for independently prepared electrodes, which allows the possibility of commercial production and factory calibration. The principles of using multiple electrodes modified with recognition elements with different affinities for the target analyte to extend the dynamic range of sensors is a general one that could be applied to other analytes.

CEACAM1 (CD66a) promotes human monocyte survival via a phosphatidylinositol 3-kinase- and AKT-dependent pathway.

CEACAM1 (also known as CD66a) is a transmembrane glycoprotein that mediates homophilic intercellular interactions that influence cellular growth, immune cell activation, and tissue morphogenesis. Various studies have suggested a link between CEACAM1 and cellular apoptosis, including a recent demonstration that ERK1/2 signaling is triggered downstream of CEACAM1. In this study, we reveal that CEACAM1-long binding confers survival signals to human peripheral blood mononuclear cells. CEACAM-specific antibodies effectively protected peripheral blood mononuclear cells from apoptosis, with this effect being particularly dramatic for primary monocytes that undergo spontaneous apoptosis during in vitro culture. This protective effect was reiterated when using soluble CEACAM1, which binds to cell-surface CEACAM1 via homophilic interactions. Monocyte survival correlated with a CEACAM1-dependent up-regulation of the cellular inhibitor of apoptosis Bcl-2 and the abrogation of caspase-3 activation. CEACAM1 binding triggered a phosphatidylinositol 3-kinase-dependent activation of the protein kinase Akt without influencing the activity of extracellular signal-related kinase ERK, whereas the phosphatidylinositol 3-kinase-specific inhibitor LY294002 effectively blocked the protective effect of CEACAM1. Together, this work indicates that CEACAM1 confers a phosphatidylinositol 3-kinase- and Akt-dependent survival signal that inhibits mitochondrion-dependent apoptosis of monocytes. By controlling both ERK/MEK and PI3K/Akt pathways, CEACAM1 functions as a key regulator of contact-dependent control of cell survival, differentiation, and growth.

Application of N-PLS calibration to the simultaneous determination of Cu(2+), Cd(2+) and Pb(2+) using peptide modified electrochemical sensors.

The simultaneous determination of Cu(2+), Cd(2+) and Pb(2+) is demonstrated at four modified gold electrodes using N-PLS calibration. Three of the electrodes were modified with the peptides Gly-Gly-His, gamma-Glu-Cys Gly and human angiotensin I which were covalently attached to thioctic acid self-assembled monolayers and the fourth electrode was modified with thioctic acid only. Voltammetry at the modified electrodes in the presence of the three metal ions revealed one peak due to the reduction of copper and another due to the overlapping peaks of cadmium and lead which made quantification using conventional methods difficult. N-PLS was used to calibrate and predict trace concentrations (100 nM to 10 microM) of mixtures of Cu(2+), Cd(2+) and Pb(2+).