Displaying publications 1 - 20 of 28 in total

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  1. Han H, Sabani NB, Nobusawa K, Takei F, Nakatani K, Yamashita I
    Anal Chem, 2023 Jul 04;95(26):9729-9733.
    PMID: 37341999 DOI: 10.1021/acs.analchem.3c01126
    We have developed a DNA sensor that can be finalized to detect a specific target on demand. The electrode surface was modified with 2,7-diamino-1,8-naphthyridine (DANP), a small molecule with nanomolar affinity for the cytosine bulge structure. The electrode was immersed in a solution of synthetic probe-DNA that had a cytosine bulge structure at one end and a complementary sequence to the target DNA at the other end. The strong binding between the cytosine bulge and DANP anchored the probe DNAs to the electrode surface, and the electrode became ready for target DNA sensing. The complementary sequence portion of the probe DNA can be changed as requested, allowing for the detection of a wide variety of targets. Electrochemical impedance spectroscopy (EIS) with the modified electrode detected target DNAs with a high sensitivity. The charge transfer resistance (Rct) extracted from EIS showed a logarithmic relationship with the concentration of target DNA. The limit of detection (LoD) was less than 0.01 μM. By this method, highly sensitive DNA sensors for various target sequences could be easily produced.
  2. Choi JR, Liu Z, Hu J, Tang R, Gong Y, Feng S, et al.
    Anal Chem, 2016 06 21;88(12):6254-64.
    PMID: 27012657 DOI: 10.1021/acs.analchem.6b00195
    In nucleic acid testing (NAT), gold nanoparticle (AuNP)-based lateral flow assays (LFAs) have received significant attention due to their cost-effectiveness, rapidity, and the ability to produce a simple colorimetric readout. However, the poor sensitivity of AuNP-based LFAs limits its widespread applications. Even though various efforts have been made to improve the assay sensitivity, most methods are inappropriate for integration into LFA for sample-to-answer NAT at the point-of-care (POC), usually due to the complicated fabrication processes or incompatible chemicals used. To address this, we propose a novel strategy of integrating a simple fluidic control strategy into LFA. The strategy involves incorporating a piece of paper-based shunt and a polydimethylsiloxane (PDMS) barrier to the strip to achieve optimum fluidic delays for LFA signal enhancement, resulting in 10-fold signal enhancement over unmodified LFA. The phenomena of fluidic delay were also evaluated by mathematical simulation, through which we found the movement of fluid throughout the shunt and the tortuosity effects in the presence of PDMS barrier, which significantly affect the detection sensitivity. To demonstrate the potential of integrating this strategy into a LFA with sample-in-answer-out capability, we further applied this strategy into our prototype sample-to-answer LFA to sensitively detect the Hepatitis B virus (HBV) in clinical blood samples. The proposed strategy offers great potential for highly sensitive detection of various targets for wide application in the near future.
  3. Wong KS, Lee L, Hung YM, Yeo LY, Tan MK
    Anal Chem, 2019 10 01;91(19):12358-12368.
    PMID: 31500406 DOI: 10.1021/acs.analchem.9b02850
    Rayleigh surface acoustic waves (SAWs) have been demonstrated as a powerful and effective means for driving a wide range of microfluidic actuation processes. Traditionally, SAWs have been generated on piezoelectric substrates, although the cost of the material and the electrode deposition process makes them less amenable as low-cost and disposable components. As such, a "razor-and-blades" model that couples the acoustic energy of the SAW on the piezoelectric substrate through a fluid coupling layer and into a low-cost and, hence, disposable silicon superstrate on which various microfluidic processes can be conducted has been proposed. Nevertheless, it was shown that only bulk vibration in the form of Lamb waves can be excited in the superstrate, which is considerably less efficient and flexible in terms of microfluidic functionality compared to its surface counterpart, that is, the SAW. Here, we reveal an extremely simple way that quite unexpectedly and rather nonintuitively allows SAWs to be generated on the superstrate-by coating the superstrate with a thin gold layer. In addition to verifying the existence of the SAW on the coated superstrate, we carry out finite-difference time domain numerical simulations that not only confirm the experimental observations but also facilitate an understanding of the surprising difference that the coating makes. Finally, we elucidate the various power-dependent particle concentration phenomena that can be carried out in a sessile droplet atop the superstrate and show the possibility for simply carrying out rapid and effective microcentrifugation-a process that is considerably more difficult with Lamb wave excitation on the superstrate.
  4. Tey HY, Breadmore MC, See HH
    Anal Chem, 2023 Jan 31;95(4):2134-2139.
    PMID: 36649064 DOI: 10.1021/acs.analchem.2c02937
    A polymer inclusion membrane (PIM) based sampling probe was developed for electrokinetic extraction of drugs from biological fluids. The probe was fabricated by dip-coating a nonconductive glass capillary tube in a homogeneous PIM solution for three cycles. The PIM solution comprised cellulose triacetate (CTA), 2-nitrophenyl octyl ether (NPOE), and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [EMIM][NTf2] in a ratio of 5:4:2. The developed probe electrokinetically extracted doxorubicin from human plasma, human serum, and dried blood spot (DBS). The practicability and reliability of the electrokinetic extraction were evaluated by LC-MS/MS to quantify the desorption of extracted doxorubicin. Under the optimized conditions, a quantification limit of 0.2-2 ng/mL was achieved for the three biological samples. The probe was further integrated into a portable battery-powered device for safe low-voltage (36 V) electrokinetic extraction. The developed technique is envisioned to provide a more efficient analytical workflow in the laboratory.
  5. Makhsin SR, Goddard NJ, Gupta R, Gardner P, Scully PJ
    Anal Chem, 2020 11 17;92(22):14907-14914.
    PMID: 32378876 DOI: 10.1021/acs.analchem.0c00586
    The metal-clad leaky waveguide (MCLW) is an optical biosensor consisting of a metal layer and a low index waveguide layer on a glass substrate. This label-free sensor measures refractive index (RI) changes within the waveguide layer. This work shows the development and optimization of acrylate based-hydrogel as the waveguide layer formed from PEG diacrylate (PEGDA, Mn 700), PEG methyl ether acrylate (PEGMEA, Mn 480), and acrylate-PEG2000-NHS fabricated on a substrate coated with 9.5 nm of titanium. The acrylate-based hydrogel is a synthetic polymer, so properties such as optical transparency, porosity, and hydrogel functionalization by a well-controlled reactive group can be tailored for immobilization of the bioreceptor within the hydrogel matrix. The waveguide sensor demonstrated an equal response to solutions of identical RI containing small (glycerol) and large (bovine serum albumin; BSA) analyte molecules, indicating that the hydrogel waveguide film is highly porous to both sizes of molecule, thus potentially allowing penetration of a range of analytes within the porous matrix. The final optimized MCLW chip was formed from a total hydrogel concentration of 40% v/v of PEGMEA-PEGDA (Mn 700), functionalized with 2.5% v/v of acrylate-PEG2000-NHS. The sensor generated a single-moded waveguide signal with a RI sensitivity of 128.61 ± 0.15° RIU-1 and limit of detection obtained at 2.2 × 10-6 RIU with excellent signal-to-noise ratio for the glycerol detection. The sensor demonstrated RI detection by monitoring changes in the out-coupled angle resulting from successful binding of d-biotin to streptavidin immobilized on functionalized acrylate hydrogel, generating a binding signal of (12.379 ± 0.452) × 10-3°.
  6. Leo BF, Fearn S, Gonzalez-Cater D, Theodorou I, Ruenraroengsak P, Goode AE, et al.
    Anal Chem, 2019 Sep 03;91(17):11098-11107.
    PMID: 31310103 DOI: 10.1021/acs.analchem.9b01704
    There are no methods sensitive enough to detect enzymes within cells, without the use of analyte labeling. Here we show that it is possible to detect protein ion signals of three different H2S-synthesizing enzymes inside microglia after pretreatment with silver nanowires (AgNW) using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Protein fragment ions, including the fragment of amino acid (C4H8N+ = 70 amu), fragments of the sulfur-producing cystathionine-containing enzymes, and the Ag+ ion signal could be detected without the use of any labels; the cells were mapped using the C4H8N+ amino acid fragment. Scanning electron microscopy imaging and energy-dispersive X-ray chemical analysis showed that the AgNWs were inside the same cells imaged by TOF-SIMS and transformed chemically into crystalline Ag2S within cells in which the sulfur-producing proteins were detected. The presence of these sulfur-producing cystathionine-containing enzymes within the cells was confirmed by Western blots and confocal microscopy images of fluorescently labeled antibodies against the sulfur-producing enzymes. Label-free TOF-SIMS is very promising for the label-free identification of H2S-contributing enzymes and their cellular localization in biological systems. The technique could in the future be used to identify which of these enzymes are most contributory.
  7. Yean CY, Kamarudin B, Ozkan DA, Yin LS, Lalitha P, Ismail A, et al.
    Anal Chem, 2008 Apr 15;80(8):2774-9.
    PMID: 18311943 DOI: 10.1021/ac702333x
    A general purpose enzyme-based amperometric electrochemical genosensor assay was developed wherein polymerase chain reaction (PCR) amplicons labeled with both biotin and fluorescein were detected with peroxidase-conjugated antifluorescein antibody on a screen-printed carbon electrode (SPCE). As a proof of principle, the response selectivity of the genosensor was evaluated using PCR amplicons derived from lolB gene of Vibrio cholerae. Factors affecting immobilization, hybridization, and nonspecific binding were optimized to maximize sensitivity and reduce assay time. On the basis of the background amperometry signals obtained from nonspecific organisms and positive signals obtained from known V. cholerae, a threshold point of 4.20 microA signal was determined as positive. Under the optimum conditions, the limit of detection (LOD) of the assay was 10 CFU/mL of V. cholerae. The overall precision of this assay was good, with the coefficient of variation (CV) being 3.7% using SPCE and intermittent pulse amperometry (IPA) as an electrochemical technique. The assay is sensitive, safe, and cost-effective when compared to conventional agarose gel electrophoresis, real-time PCR, and other enzyme-linked assays for the detection of PCR amplicons. Furthermore, the use of a hand-held portable reader makes it suitable for use in the field.
  8. Wang Y, Liu X, Dong L, Cheng KK, Lin C, Wang X, et al.
    Anal Chem, 2023 Apr 18;95(15):6203-6211.
    PMID: 37023366 DOI: 10.1021/acs.analchem.2c04603
    Drug combinations are commonly used to treat various diseases to achieve synergistic therapeutic effects or to alleviate drug resistance. Nevertheless, some drug combinations might lead to adverse effects, and thus, it is crucial to explore the mechanisms of drug interactions before clinical treatment. Generally, drug interactions have been studied using nonclinical pharmacokinetics, toxicology, and pharmacology. Here, we propose a complementary strategy based on metabolomics, which we call interaction metabolite set enrichment analysis, or iMSEA, to decipher drug interactions. First, a digraph-based heterogeneous network model was constructed to model the biological metabolic network based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Second, treatment-specific influences on all detected metabolites were calculated and propagated across the whole network model. Third, pathway activity was defined and enriched to quantify the influence of each treatment on the predefined functional metabolite sets, i.e., metabolic pathways. Finally, drug interactions were identified by comparing the pathway activity enriched by the drug combination treatments and the single drug treatments. A data set consisting of hepatocellular carcinoma (HCC) cells that were treated with oxaliplatin (OXA) and/or vitamin C (VC) was used to illustrate the effectiveness of the iMSEA strategy for evaluation of drug interactions. Performance evaluation using synthetic noise data was also performed to evaluate sensitivities and parameter settings for the iMSEA strategy. The iMSEA strategy highlighted synergistic effects of combined OXA and VC treatments including the alterations in the glycerophospholipid metabolism pathway and glycine, serine, and threonine metabolism pathway. This work provides an alternative method to reveal the mechanisms of drug combinations from the viewpoint of metabolomics.
  9. Thang LY, See HH, Quirino JP
    Anal Chem, 2016 Sep 26.
    PMID: 27669824
    The translation of stacking techniques used in capillary electrophoresis (CE) to microchip CE (MCE) in order to improve concentration sensitivity is an important area of study. The success in stacking relies on the generation and control of the stacking boundaries which is a challenge in MCE because the manipulation of solutions is not as straightforward as in CE with a single channel. Here, a simple and rapid on-line sample concentration (stacking strategy) in a battery operated nonaqueous MCE device with a commercially available double T-junction glass chip is presented. A multi-stacking approach was developed in order to circumvent the issues for stacking in nonaqueous MCE. The cationic analytes from the two loading channels were injected under field-enhanced conditions and were focused by micelle-to-solvent stacking. This was achieved by the application of high electric fields along the two loading channels and a low electric field in the separation channel, with one ground electrode in the reservoir closest to the junction. At the junction, the stacked zones were re-stacked under field-enhanced conditions and then injected into the separation channels. The multi-stacking was verified under a fluorescence microscope using Rhodamine 6G as the analyte, revealing a sensitivity enhancement factor (SEF) of 110. The stacking approach was also implemented in the nonaqueous MCE with contactless conductivity detection of the anticancer drug tamoxifen as well as its metabolites. The multi-stacking and analysis time was 40 s and 110 s, respectively, the limit of detections was from 10 to 35 ng/mL, and the SEFs were 20 to 50. The method was able to quantify the target analytes from breast cancer patients.
  10. Zhao L, Wang Q, Cui X, Li H, Zhao L, Wang Z, et al.
    Anal Chem, 2024 Feb 06;96(5):1913-1921.
    PMID: 38266028 DOI: 10.1021/acs.analchem.3c04062
    2D nanosheets (NSs) have been widely used in drug-related applications. However, a comprehensive investigation into the cytotoxicity mechanism linked to the redox activity is lacking. In this study, with cytochrome c (Cyt c) as the model biospecies, the cytotoxicity of 2D NSs was evaluated systematically based on their redox effect with microfluidic techniques. The interface interaction, dissolution, and redox effect of 2D NSs on Cyt c were monitored with pulsed streaming potential (SP) measurement and capillary electrophoresis (CE). The relationship between the redox activity of 2D NSs and the function of Cyt c was evaluated in vitro with Hela cells. The results indicated that the dissolution and redox activity of 2D NSs can be simultaneously monitored with CE under weak interface interactions and at low sample volumes. Both WS2 NSs and MoS2 NSs can reduce Cyt c without significant dissolution, with reduction rates measured at 6.24 × 10-5 M for WS2 NSs and 3.76 × 10-5 M for MoS2 NSs. Furthermore, exposure to 2D NSs exhibited heightened reducibility, which prompted more pronounced alterations associated with Cyt c dysfunction, encompassing ATP synthesis, modifications in mitochondrial membrane potential, and increased reactive oxygen species production. These observations suggest a positive correlation between the redox activity of 2D NSs and their redox toxicity in Hela cells. These findings provide valuable insight into the redox properties of 2D NSs regarding cytotoxicity and offer the possibility to modify the 2D NSs to reduce their redox toxicity for clinical applications.
  11. Joshi P, Okada T, Miyabayashi K, Miyake M
    Anal Chem, 2018 May 15;90(10):6116-6123.
    PMID: 29613775 DOI: 10.1021/acs.analchem.8b00247
    Organically (octyl amine, OA) surface modified electrocatalyst (OA-Pt/CB) was studied for its oxygen reduction reaction (ORR) activity via dc methods and its charge and mass transfer properties were studied via electrochemical impedance spectroscopy (EIS). Comparison with a commercial catalyst (TEC10V30E) with similar Pt content was also carried out. In EIS, both the catalysts showed a single time-constant with an emerging high-frequency semicircle of very small diameter which was fitted using suitable equivalent circuits. The organically modified catalyst showed lower charge-transfer resistance and hence, low polarization resistance in high potential region as compared to the commercial catalyst. The dominance of kinetic processes was observed at 0.925-1.000 V, whereas domination of diffusion based processes was observed at lower potential region for the organic catalyst. No effect due to the presence of carbon was observed in the EIS spectra. Using the hydrodynamic method, higher current penetration depth was obtained for the organically modified catalyst at 1600 rpm. Exchange current density and Tafel slopes for both the electrocatalysts were calculated from the polarization resistance obtained from EIS which was in correlation with the results obtained from dc methods.
  12. Yan D, Wong YF, Whittock SP, Koutoulis A, Shellie RA, Marriott PJ
    Anal Chem, 2018 04 17;90(8):5264-5271.
    PMID: 29575899 DOI: 10.1021/acs.analchem.8b00142
    A novel sequential three-dimensional gas chromatography-high-resolution time-of-flight mass spectrometry (3D GC-accTOFMS) approach for profiling secondary metabolites in complex plant extracts is described. This integrated system incorporates a nonpolar first-dimension (1Dnp) separation step, prior to a microfluidic heart-cut (H/C) of a targeted region(s) to a cryogenic trapping device, directly followed by the rapid reinjection of a trapped solute into a polar second-dimension (2DPEG) column for multidimensional separation (GCnp-GCPEG). For additional separation, the effluent from 2DPEG can then be modulated according to a comprehensive 2D GC process (GC×GC), using an ionic liquid phase as a third-dimension (3DIL) column, to produce a sequential GCnp-GCPEG×GCIL separation. Thus, the unresolved or poorly resolved components, or regions that require further separation, can be precisely selected and rapidly transferred for additional separation on 2D or 3D columns, based on the greater separation realized by these steps. The described integrated system can be used in a number of modes, but one useful approach is to target specific classes of compounds for improved resolution. This is demonstrated through the separation and detection of the oxygenated sesquiterpenes in hop ( Humulus lupulus L.) essential oil and agarwood ( Aquilaria malaccensis) oleoresin. Improved resolution and peak capacity were illustrated through the progressive comparison of the tentatively identified components for GCnp-GCPEG and GCnp-GCPEG×GCIL methods. Relative standard deviations of intraday retentions (1 tR, 2 tR,, and 3 tR) and peak areas of ≤0.01, 0.07, 0.71, and 7.5% were achieved. This analytical approach comprising three GC column selectivities, hyphenated with high-resolution TOFMS detection, should be a valuable adjunct for the improved characterization of complex plant samples, particularly in the area of plant metabolomics.
  13. Zheng J, Wai JL, Lake RJ, New SY, He Z, Lu Y
    Anal Chem, 2021 08 10;93(31):10834-10840.
    PMID: 34310132 DOI: 10.1021/acs.analchem.1c01077
    DNAzymes have emerged as an important class of sensors for a wide variety of metal ions, with florescence DNAzyme sensors as the most widely used in different sensing and imaging applications because of their fast response time, high signal intensity, and high sensitivity. However, the requirements of an external excitation light source and its associated power increase the cost and size of the fluorometer, making it difficult to be used for portable detections. To overcome these limitations, we report herein a DNAzyme sensor that relies on chemiluminescence resonance energy transfer (CRET) without the need for external light. The sensor is constructed by combining the functional motifs from both Pb2+-dependent 8-17 DNAzyme conjugated to fluorescein (FAM) and hemin/G-quadruplex that mimics horseradish peroxidase to catalyze the oxidation of luminol by H2O2 to yield chemiluminescence. In the absence of Pb2+, the hybridization between the enzyme and substrate strands bring the FAM and hemin/G-quadruplex in close proximity, resulting in CRET. The presence of Pb2+ ions can drive the cleavage on the substrate strand, resulting in a sharp decrease in the melting temperature of hybridization and thus separation of the FAM from hemin/G-quadruplex. The liberated CRET pair causes a ratiometric increase in the donor's fluorescent signal and a decrease in the acceptor signal. Using this method, Pb2+ ions have been measured rapidly (<15 min) with a low limit of detection at 5 nM. By removing the requirement of exogenous light excitation, we have demonstrated a simple and portable detection using a smartphone, making the DNAzyme-CRET system suitable for field tests of lake water. Since DNAzymes selective for other metal ions or targets, such as bacteria, can be obtained using in vitro selection, the method reported here opens a new avenue for rapid, portable, and ratiometric detection of many targets in environmental monitoring, food safety, and medical diagnostics.
  14. Shi J, Zhao J, Zhang Y, Wang Y, Tan CP, Xu YJ, et al.
    Anal Chem, 2023 Dec 26;95(51):18793-18802.
    PMID: 38095040 DOI: 10.1021/acs.analchem.3c03785
    Metabolomics and proteomics offer significant advantages in understanding biological mechanisms at two hierarchical levels. However, conventional single omics analysis faces challenges due to the high demand for specimens and the complexity of intrinsic associations. To obtain comprehensive and accurate system biological information, we developed a multiomics analytical method called Windows Scanning Multiomics (WSM). In this method, we performed simultaneous extraction of metabolites and proteins from the same sample, resulting in a 10% increase in the coverage of the identified biomolecules. Both metabolomics and proteomics analyses were conducted by using ultrahigh-performance liquid chromatography mass spectrometry (UPLC-MS), eliminating the need for instrument conversions. Additionally, we designed an R-based program (WSM.R) to integrate mathematical and biological correlations between metabolites and proteins into a correlation network. The network created from simultaneously extracted biomolecules was more focused and comprehensive compared to those from separate extractions. Notably, we excluded six pairs of false-positive relationships between metabolites and proteins in the network established using simultaneously extracted biomolecules. In conclusion, this study introduces a novel approach for multiomics analysis and data processing that greatly aids in bioinformation mining from multiomics results. This method is poised to play an indispensable role in systems biology research.
  15. Promja S, Puenpa J, Achakulvisut T, Poovorawan Y, Lee SY, Athamanolap P, et al.
    Anal Chem, 2023 Jan 12.
    PMID: 36633573 DOI: 10.1021/acs.analchem.2c05112
    Since the declaration of COVID-19 as a pandemic in early 2020, multiple variants of the severe acute respiratory syndrome-related coronavirus (SARS-CoV-2) have been detected. The emergence of multiple variants has raised concerns due to their impact on public health. Therefore, it is crucial to distinguish between different viral variants. Here, we developed a machine learning web-based application for SARS-CoV-2 variant identification via duplex real-time polymerase chain reaction (PCR) coupled with high-resolution melt (qPCR-HRM) analysis. As a proof-of-concept, we investigated the platform's ability to identify the Alpha, Delta, and wild-type strains using two sets of primers. The duplex qPCR-HRM could identify the two variants reliably in as low as 100 copies/μL. Finally, the platform was validated with 167 nasopharyngeal swab samples, which gave a sensitivity of 95.2%. This work demonstrates the potential for use as automated, cost-effective, and large-scale viral variant surveillance.
  16. Samat N, Tan PJ, Shaari K, Abas F, Lee HB
    Anal Chem, 2014 Feb 4;86(3):1324-31.
    PMID: 24405504 DOI: 10.1021/ac403709a
    Photodynamic therapy (PDT) is an alternative treatment for cancer that involves administration of a photosensitive drug or photosensitizer that localizes at the tumor tissue followed by in situ excitation at an appropriate wavelength of light. Tumour tissues are then killed by cytotoxic reactive oxygen species generated by the photosensitizer. Targeted excitation and photokilling of affected tissues is achieved through focal light irradiation, thereby minimizing systemic side effects to the normal healthy tissues. Currently, there are only a small number of photosensitizers that are in the clinic and many of these share the same structural core based on cyclic tetrapyrroles. This paper describes how metabolic tools are utilized to prioritize natural extracts to search for structurally new photosensitizers from Malaysian biodiversity. As proof of concept, we analyzed 278 photocytotoxic extracts using a hyphenated technique of liquid chromatography-mass spectrometry coupled with principal component analysis (LC-MS-PCA) and prioritized 27 extracts that potentially contained new photosensitizers for chemical dereplication using an in-house UPLC-PDA-MS-Photocytotoxic assay platform. This led to the identification of 2 new photosensitizers with cyclic tetrapyrrolic structures, thereby demonstrating the feasibility of the metabolic approach.
  17. Okazaki T, Orii T, Tan SY, Watanabe T, Taguchi A, Rahman FA, et al.
    Anal Chem, 2020 07 21;92(14):9714-9721.
    PMID: 32551577 DOI: 10.1021/acs.analchem.0c01062
    We present an electrochemical long period fiber grating (LPFG) sensor for electroactive species with an optically transparent electrode. The sensor was fabricated by coating indium tin oxide onto the surface of LPFG using a polygonal barrel-sputtering method. LPFG was produced by an electric arc-induced technique. The sensing is based on change in the detection of electron density on the electrode surface during potential application and its reduction by electrochemical redox of analytes. Four typical electroactive species of methylene blue, hexaammineruthenium(III), ferrocyanide, and ferrocenedimethanol were used to investigate the sensor performance. The concentrations of analytes were determined by the modulation of the potential as the change in transmittance around the resonance band of LPFG. The sensitivity of the sensor, particularly to methylene blue, was high, and the sensor responded to a wide concentration range of 0.001 mM to 1 mM.
  18. Tu Y, Ahmad N, Briscoe J, Zhang DW, Krause S
    Anal Chem, 2018 07 17;90(14):8708-8715.
    PMID: 29932632 DOI: 10.1021/acs.analchem.8b02244
    Light-addressable potentiometric sensors (LAPS) are of great interest in bioimaging applications such as the monitoring of concentrations in microfluidic channels or the investigation of metabolic and signaling events in living cells. By measuring the photocurrents at electrolyte-insulator-semiconductor (EIS) and electrolyte-semiconductor structures, LAPS can produce spatiotemporal images of chemical or biological analytes, electrical potentials and impedance. However, its commercial applications are often restricted by their limited AC photocurrents and resolution of LAPS images. Herein, for the first time, the use of 1D semiconducting oxides in the form of ZnO nanorods for LAPS imaging is explored to solve this issue. A significantly increased AC photocurrent with enhanced image resolution has been achieved based on ZnO nanorods, with a photocurrent of 45.7 ± 0.1 nA at a light intensity of 0.05 mW, a lateral resolution as low as 3.0 μm as demonstrated by images of a PMMA dot on ZnO nanorods and a pH sensitivity of 53 mV/pH. The suitability of the device for bioanalysis and bioimaging was demonstrated by monitoring the degradation of a thin poly(ester amide) film with the enzyme α-chymotrypsin using LAPS. This simple and robust route to fabricate LAPS substrates with excellent performance would provide tremendous opportunities for bioimaging.
  19. Ng KL, Khor SM
    Anal Chem, 2017 09 19;89(18):10004-10012.
    PMID: 28845664 DOI: 10.1021/acs.analchem.7b02432
    Guanine (G), adenine (A), thymine (T), and cytosine (C) are the four basic constituents of DNA. Studies on DNA composition have focused especially on DNA damage and genotoxicity. However, the development of a rapid, simple, and multiplex method for the simultaneous measurement of the four DNA bases remains a challenge. In this study, we describe a graphite-based nanocomposite electrode (Au-rGO/MWCNT/graphite) that uses a simple electro-co-deposition approach. We successfully applied the developed sensor for multiplex detection of G, A, T, and C, using square-wave voltammetry. The sensor was tested using real animal and plant DNA samples in which the hydrolysis of T and C could be achieved with 8 mol L-1 of acid. The electrochemical sensor exhibited excellent sensitivity (G = 178.8 nA/μg mL-1, A = 92.9 nA/μg mL-1, T = 1.4 nA/μg mL-1, and C = 15.1 9 nA/μg mL-1), low limit of detection (G, A = 0.5 μg mL-1; T, C = 1.0 μg mL-1), and high selectivity in the presence of common interfering factors from biological matrixes. The reliability of the established method was assessed by method validation and comparison with the ultraperformance liquid chromatography technique, and a correlation of 103.7% was achieved.
  20. Jajuli MN, Hussin MH, Saad B, Rahim AA, Hébrant M, Herzog G
    Anal Chem, 2019 06 04;91(11):7466-7473.
    PMID: 31050400 DOI: 10.1021/acs.analchem.9b01674
    A new sample preparation method is proposed for the extraction of pharmaceutical compounds (Metformin, Phenyl biguanide, and Phenformin) of varied hydrophilicity, dissolved in an aqueous sample. When in contact with an organic phase, an interfacial potential is imposed by the presence of an ion, tetramethylammonium (TMA+), common to each phase. The interfacial potential difference drives the transfer of ionic analytes across the interface and allows it to reach up to nearly 100% extraction efficiency and a 60-fold enrichment factor in optimized extraction conditions as determined by HPLC analysis.
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