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Using a photochemical method and chitosan to prepare surface-enhanced Raman scattering–active silver nanoparticles
15 May 2012,
17:58:58
Publication year:
2012
Source:Analytica Chimica Acta, Volume 729
Kuang-Hsuan Yang, Chia-Ming Chang
In this paper, we report a new strategy for the preparation of surface-enhanced Raman scattering (SERS)-active silver nanoparticles (Ag NPs), using a photochemical method and the presence of chitosan (Ch). First, Ag substrates were subjected to electrochemical oxidation/reduction cycles (ORCs) in deoxygenated aqueous solutions containing 0.1M HNO3 and 1gL−1 Ch (pH 6.9, adjusted by adding 1M NaOH), resulting in Ag+–Ch complexes. These substrates were then irradiated with UV light at various wavelengths to yield the SERS-active Ag NPs. A stronger SERS effect was observed on the SERS-active Ag NPs prepared by using UV irradiation at 310nm. The pH of the solution and the presence of Ch during the preparation process both affected the resulting SERS activities.
Source:Analytica Chimica Acta, Volume 729
Kuang-Hsuan Yang, Chia-Ming Chang
In this paper, we report a new strategy for the preparation of surface-enhanced Raman scattering (SERS)-active silver nanoparticles (Ag NPs), using a photochemical method and the presence of chitosan (Ch). First, Ag substrates were subjected to electrochemical oxidation/reduction cycles (ORCs) in deoxygenated aqueous solutions containing 0.1M HNO3 and 1gL−1 Ch (pH 6.9, adjusted by adding 1M NaOH), resulting in Ag+–Ch complexes. These substrates were then irradiated with UV light at various wavelengths to yield the SERS-active Ag NPs. A stronger SERS effect was observed on the SERS-active Ag NPs prepared by using UV irradiation at 310nm. The pH of the solution and the presence of Ch during the preparation process both affected the resulting SERS activities.
Graphical Abstract
Graphical abstract Highlights
SEM images of Ag NPs obtained after reducing Ag+-containing complexes in solutions of 0.1M HNO3 containing 1gL−1 Ch (pH 6.9, adjusted with 1M NaOH) under irradiation with UV light of wavelength of 310nm for 30min. ► Prepare SERS-active Ag nanoparticles by using green process with aid of chitosan. ► The Ag-containing complex was irradiated with UV light to yield SERS activity. ► pH of the solution and the presence of Ch both affect the resulting SERS activities.Determination of inorganic phosphate by electroanalytical methods: A review
15 May 2012,
17:58:58
Publication year:
2012
Source:Analytica Chimica Acta, Volume 729
Sheela Berchmans, Touma B. Issa, Pritam Singh
Determination of inorganic phosphate is of very high importance in environmental and health care applications. Hence knowledge of suitable analytical techniques available for phosphate sensing for different applications becomes essential. Electrochemical methods for determining inorganic phosphate have several advantages over other common techniques, including detection selectivity, stability and relative environmental insensitivity of electroactive labels. The different electrochemical sensing strategies adopted for the determination of phosphate using selective ionophores are discussed in this review. The various sensing strategies are classified based on the electrochemical detection techniques used viz., potentiometry, voltammetry, amperometry, unconventional electrochemical methods etc., The enzymatic sensing of phosphate coupled with electrochemical detection is also included. Various electroanalytical methods available in the literature are assessed for their merits in terms of selectivity, simplicity, miniaturisation, adaptability and suitability for field measurements.
Source:Analytica Chimica Acta, Volume 729
Sheela Berchmans, Touma B. Issa, Pritam Singh
Determination of inorganic phosphate is of very high importance in environmental and health care applications. Hence knowledge of suitable analytical techniques available for phosphate sensing for different applications becomes essential. Electrochemical methods for determining inorganic phosphate have several advantages over other common techniques, including detection selectivity, stability and relative environmental insensitivity of electroactive labels. The different electrochemical sensing strategies adopted for the determination of phosphate using selective ionophores are discussed in this review. The various sensing strategies are classified based on the electrochemical detection techniques used viz., potentiometry, voltammetry, amperometry, unconventional electrochemical methods etc., The enzymatic sensing of phosphate coupled with electrochemical detection is also included. Various electroanalytical methods available in the literature are assessed for their merits in terms of selectivity, simplicity, miniaturisation, adaptability and suitability for field measurements.
Graphical Abstract
Graphical abstract Highlights
► Advantages of electrochemical sensing of phosphate. ► Classification of electrochemical methods of sensing. ► Ionophores for potentiometric sensing of phosphate. ► Supramolecular based sensing of phosphate: voltammetry and amperometry. ► Unconventional and indirect methods of sensing phosphate.Direct rapid analysis of trace bioavailable soil macronutrients by chemometrics-assisted energy dispersive X-ray fluorescence and scattering spectrometry
15 May 2012,
17:58:58
Publication year:
2012
Source:Analytica Chimica Acta, Volume 729
M.I. Kaniu, K.H. Angeyo, A.K. Mwala, M.J. Mangala
Precision agriculture depends on the knowledge and management of soil quality (SQ), which calls for affordable, simple and rapid but accurate analysis of bioavailable soil nutrients. Conventional SQ analysis methods are tedious and expensive. We demonstrate the utility of a new chemometrics-assisted energy dispersive X-ray fluorescence and scattering (EDXRFS) spectroscopy method we have developed for direct rapid analysis of trace ‘bioavailable’ macronutrients (i.e. C, N, Na, Mg, P) in soils. The method exploits, in addition to X-ray fluorescence, the scatter peaks detected from soil pellets to develop a model for SQ analysis. Spectra were acquired from soil samples held in a Teflon holder analyzed using 109Cd isotope source EDXRF spectrometer for 200s. Chemometric techniques namely principal component analysis (PCA), partial least squares (PLS) and artificial neural networks (ANNs) were utilized for pattern recognition based on fluorescence and Compton scatter peaks regions, and to develop multivariate quantitative calibration models based on Compton scatter peak respectively. SQ analyses were realized with high CMD (R 2 >0.9) and low SEP (0.01% for N and Na, 0.05% for C, 0.08% for Mg and 1.98μgg−1 for P). Comparison of predicted macronutrients with reference standards using a one-way ANOVA test showed no statistical difference at 95% confidence level. To the best of the authors’ knowledge, this is the first time that an XRF method has demonstrated utility in trace analysis of macronutrients in soil or related matrices.
Source:Analytica Chimica Acta, Volume 729
M.I. Kaniu, K.H. Angeyo, A.K. Mwala, M.J. Mangala
Precision agriculture depends on the knowledge and management of soil quality (SQ), which calls for affordable, simple and rapid but accurate analysis of bioavailable soil nutrients. Conventional SQ analysis methods are tedious and expensive. We demonstrate the utility of a new chemometrics-assisted energy dispersive X-ray fluorescence and scattering (EDXRFS) spectroscopy method we have developed for direct rapid analysis of trace ‘bioavailable’ macronutrients (i.e. C, N, Na, Mg, P) in soils. The method exploits, in addition to X-ray fluorescence, the scatter peaks detected from soil pellets to develop a model for SQ analysis. Spectra were acquired from soil samples held in a Teflon holder analyzed using 109Cd isotope source EDXRF spectrometer for 200s. Chemometric techniques namely principal component analysis (PCA), partial least squares (PLS) and artificial neural networks (ANNs) were utilized for pattern recognition based on fluorescence and Compton scatter peaks regions, and to develop multivariate quantitative calibration models based on Compton scatter peak respectively. SQ analyses were realized with high CMD (R 2 >0.9) and low SEP (0.01% for N and Na, 0.05% for C, 0.08% for Mg and 1.98μgg−1 for P). Comparison of predicted macronutrients with reference standards using a one-way ANOVA test showed no statistical difference at 95% confidence level. To the best of the authors’ knowledge, this is the first time that an XRF method has demonstrated utility in trace analysis of macronutrients in soil or related matrices.
Graphical Abstract
Graphical abstract Highlights
► Chemometrics-assisted EDXRFS spectroscopy realizes direct, rapid and accurate analysis of trace bioavailable macronutrients in soils. ► The method is minimally invasive, involves little sample preparation, short analysis times and is relatively insensitive to matrix effects. ► This opens up the ability to rapidly characterize large number of samples/matrices with this method.Mesoporous TiO2 aerogel for selective enrichment of phosphopeptides in rat liver mitochondria
15 May 2012,
17:58:58
Publication year:
2012
Source:Analytica Chimica Acta, Volume 729
Liyuan Zhang, Zhen Liang, Kaiguang Yang, Simin Xia, Qi Wu, Lihua Zhang, Yukui Zhang
The enrichment of low abundance phosphopeptides before MS analysis is a critical step for in-depth phosphoproteome research. In this study, mesoporous titanium dioxide (TiO2) aerogel was prepared by precipitation and supercritical drying. The specific surface area up to 490.7m2 g−1 is achieved by TiO2 aerogel, much higher than those obtained by commercial TiO2 nanoparticles and by the latest reported mesoporous TiO2 spheres. Due to the large specific surface area and the mesoporous structure of the aerogel, the binding capacity for phosphopeptides is six times higher than that of conventional TiO2 microparticles (173 vs 28μmolg−1). Because of the good compatibility of enrichment procedure with MALDI-TOF-MS and the large binding capacity of TiO2 aerogel, a detection limit as low as 30amol for analyzing phosphopeptides in β-casein digest was achieved. TiO2 aerogel was further applied to enrich phosphopeptides from rat liver mitochondria, and 266 unique phosphopeptides with 340 phosphorylation sites, corresponding to 216 phosphoprotein groups, were identified by triplicate nanoRPLC-ESI-MS/MS runs, with false-positive rate less than 1% at the peptide level. These results demonstrate that TiO2 aerogel is a kind of promising material for sample pretreatment in the large-scale phosphoproteome study.
Source:Analytica Chimica Acta, Volume 729
Liyuan Zhang, Zhen Liang, Kaiguang Yang, Simin Xia, Qi Wu, Lihua Zhang, Yukui Zhang
The enrichment of low abundance phosphopeptides before MS analysis is a critical step for in-depth phosphoproteome research. In this study, mesoporous titanium dioxide (TiO2) aerogel was prepared by precipitation and supercritical drying. The specific surface area up to 490.7m2 g−1 is achieved by TiO2 aerogel, much higher than those obtained by commercial TiO2 nanoparticles and by the latest reported mesoporous TiO2 spheres. Due to the large specific surface area and the mesoporous structure of the aerogel, the binding capacity for phosphopeptides is six times higher than that of conventional TiO2 microparticles (173 vs 28μmolg−1). Because of the good compatibility of enrichment procedure with MALDI-TOF-MS and the large binding capacity of TiO2 aerogel, a detection limit as low as 30amol for analyzing phosphopeptides in β-casein digest was achieved. TiO2 aerogel was further applied to enrich phosphopeptides from rat liver mitochondria, and 266 unique phosphopeptides with 340 phosphorylation sites, corresponding to 216 phosphoprotein groups, were identified by triplicate nanoRPLC-ESI-MS/MS runs, with false-positive rate less than 1% at the peptide level. These results demonstrate that TiO2 aerogel is a kind of promising material for sample pretreatment in the large-scale phosphoproteome study.
Graphical Abstract
Graphical abstract Highlights
► The specific surface area of TiO2 aerogel is 10 times larger than TiO2 nanoparticle. ► The limit of detection for phosphopeptides was down to 30amol by TiO2 aerogel. ► The loading capacity for phosphopeptides was 6-fold larger than TiO2 microparticle.Selective trace analysis of chloroacetamide herbicides in food samples using dummy molecularly imprinted solid phase extraction based on chemometrics and quantum chemistry
15 May 2012,
17:58:58
Publication year:
2012
Source:Analytica Chimica Acta, Volume 729
Lei Zhang, Fang Han, Yanyun Hu, Ping Zheng, Xuan Sheng, Hao Sun, Wei Song, Yaning Lv
A methodology based on chemometrics and quantum chemistry was proposed to design and synthesize dummy molecularly imprinted polymers (DMIPs) capable of extracting chloroacetamide herbicides from food samples. Molecular modeling approach in conjunction with clustering analysis was used to predict the most suitable dummy template. Metolachlor deschloro was selected as the template to synthesize DMIPs, which were used as the solid phase extraction (SPE) materials. The selective adsorption of DMIPs was evaluated by high performance liquid chromatography (HPLC). The retention property of six chloroacetamide herbicides on DMIPs was also predicted using clustering analysis. The optimum loading, washing and eluting conditions for dummy molecularly imprinted solid phase extraction (DMISPE) were established to obtain high selectivity and sensitivity. Water, dichloromethane and methanol were chosen as loading, washing and elution solvent, respectively. Under optimized DMISPE conditions, recoveries of analytes were in the range of 83.4–106.7% with satisfactory precision (RSD% lower than 13%). Compared with other commercial SPE columns, DMISPE exhibited selective binding properties for chloroacetamide herbicides and the matrix effect was significantly decreased.
Source:Analytica Chimica Acta, Volume 729
Lei Zhang, Fang Han, Yanyun Hu, Ping Zheng, Xuan Sheng, Hao Sun, Wei Song, Yaning Lv
A methodology based on chemometrics and quantum chemistry was proposed to design and synthesize dummy molecularly imprinted polymers (DMIPs) capable of extracting chloroacetamide herbicides from food samples. Molecular modeling approach in conjunction with clustering analysis was used to predict the most suitable dummy template. Metolachlor deschloro was selected as the template to synthesize DMIPs, which were used as the solid phase extraction (SPE) materials. The selective adsorption of DMIPs was evaluated by high performance liquid chromatography (HPLC). The retention property of six chloroacetamide herbicides on DMIPs was also predicted using clustering analysis. The optimum loading, washing and eluting conditions for dummy molecularly imprinted solid phase extraction (DMISPE) were established to obtain high selectivity and sensitivity. Water, dichloromethane and methanol were chosen as loading, washing and elution solvent, respectively. Under optimized DMISPE conditions, recoveries of analytes were in the range of 83.4–106.7% with satisfactory precision (RSD% lower than 13%). Compared with other commercial SPE columns, DMISPE exhibited selective binding properties for chloroacetamide herbicides and the matrix effect was significantly decreased.
Graphical Abstract
Graphical abstract Highlights
► Hyperchem was used to simulate chloroacetamide herbicides and their metabolites. ► Clustering analysis was conducted to analyze the structural data. ► Metolachlor deschloro was selected as the dummy template to synthesize DMIPs. ► The elution order of herbicides on DMIPs was predicted using clustering analysis. ► Compared with other SPE columns, the matrix effect was decreased using DMISPE.Measurement of laser activated electron tunneling from semiconductor zinc oxide to adsorbed organic molecules by a matrix assisted laser desorption ionization mass spectrometer
15 May 2012,
17:58:58
Publication year:
2012
Source:Analytica Chimica Acta, Volume 729
Hongying Zhong, Jieying Fu, Xiaoli Wang, Shi Zheng
Measurement of light induced heterogeneous electron transfer is important for understanding of fundamental processes involved in chemistry, physics and biology, which is still challenging by current techniques. Laser activated electron tunneling (LAET) from semiconductor metal oxides was observed and characterized by a MALDI (matrix assisted laser desorption ionization) mass spectrometer in this work. Nanoparticles of ZnO were placed on a MALDI sample plate. Free fatty acids and derivatives were used as models of organic compounds and directly deposited on the surface of ZnO nanoparticles. Irradiation of UV laser (λ =355nm) with energy more than the band gap of ZnO produces ions that can be detected in negative mode. When TiO2 nanoparticles with similar band gap but much lower electron mobility were used, these ions were not observed unless the voltage on the sample plate was increased. The experimental results indicate that laser induced electron tunneling is dependent on the electron mobility and the strength of the electric field. Capture of low energy electrons by charge-deficient atoms of adsorbed organic molecules causes unpaired electron-directed cleavages of chemical bonds in a nonergodic pathway. In positive detection mode, electron tunneling cannot be observed due to the reverse moving direction of electrons. It should be able to expect that laser desorption ionization mass spectrometry is a new technique capable of probing the dynamics of electron tunneling. LAET offers advantages as a new ionization dissociation method for mass spectrometry.
Source:Analytica Chimica Acta, Volume 729
Hongying Zhong, Jieying Fu, Xiaoli Wang, Shi Zheng
Measurement of light induced heterogeneous electron transfer is important for understanding of fundamental processes involved in chemistry, physics and biology, which is still challenging by current techniques. Laser activated electron tunneling (LAET) from semiconductor metal oxides was observed and characterized by a MALDI (matrix assisted laser desorption ionization) mass spectrometer in this work. Nanoparticles of ZnO were placed on a MALDI sample plate. Free fatty acids and derivatives were used as models of organic compounds and directly deposited on the surface of ZnO nanoparticles. Irradiation of UV laser (λ =355nm) with energy more than the band gap of ZnO produces ions that can be detected in negative mode. When TiO2 nanoparticles with similar band gap but much lower electron mobility were used, these ions were not observed unless the voltage on the sample plate was increased. The experimental results indicate that laser induced electron tunneling is dependent on the electron mobility and the strength of the electric field. Capture of low energy electrons by charge-deficient atoms of adsorbed organic molecules causes unpaired electron-directed cleavages of chemical bonds in a nonergodic pathway. In positive detection mode, electron tunneling cannot be observed due to the reverse moving direction of electrons. It should be able to expect that laser desorption ionization mass spectrometry is a new technique capable of probing the dynamics of electron tunneling. LAET offers advantages as a new ionization dissociation method for mass spectrometry.
Graphical Abstract
Graphical abstract Highlights
► Irradiation of photons with energies more than the band gap generates electron–hole pairs. ► Electron tunneling probability is dependent on the electron mobility. ► Tunneling electrons are captured by charge deficient atoms. ► Unpaired electrons induce cleavages of chemical bonds.Small molecule analysis using laser desorption/ionization mass spectrometry on nano-coated silicon with self-assembled monolayers
15 May 2012,
17:58:58
Publication year:
2012
Source:Analytica Chimica Acta, Volume 729
Ömür Çelikbıçak, Gökhan Demirel, Erhan Pişkin, Bekir Salih
Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is an emerging technique for the determination of the molecular weight of biomolecules and their non-covalent complexes without fragmentation. One problem with this technique is the use of excess amounts of matrices, which may produce intense fragment ions and/or clusters at low mass ranges between 1 and 800Da. These fragments lead to interference, especially concerning the signals of small target molecules. Here, a simple, reusable, and quite inexpensive approach was demonstrated to improve the effectiveness of laser desorption/ionization mass spectrometry (LDI-MS) analysis, especially for small molecules, without using matrix molecules. In this study, substrates with controllable morphologies and thicknesses were developed based on the self-assembly of silane molecules on silicon surfaces using N-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA) and octadecyltrichlorosilane (OTS) molecules. Prepared substrates with nano-overlayers were successfully used in the analysis of different types of small target molecules, namely acrivastine, l-histidine, l-valine, l-phenylalanine, l-arginine, l-methionine and angiotensin I. Our substrates exhibited clear peaks almost without fragmentation for all target molecules, suggesting that these surfaces provide a number of important advantages for LDI-MS analysis, such as ease of preparation, costs, reusability, robustness, easy handling and preventing fragmentation.
Source:Analytica Chimica Acta, Volume 729
Ömür Çelikbıçak, Gökhan Demirel, Erhan Pişkin, Bekir Salih
Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is an emerging technique for the determination of the molecular weight of biomolecules and their non-covalent complexes without fragmentation. One problem with this technique is the use of excess amounts of matrices, which may produce intense fragment ions and/or clusters at low mass ranges between 1 and 800Da. These fragments lead to interference, especially concerning the signals of small target molecules. Here, a simple, reusable, and quite inexpensive approach was demonstrated to improve the effectiveness of laser desorption/ionization mass spectrometry (LDI-MS) analysis, especially for small molecules, without using matrix molecules. In this study, substrates with controllable morphologies and thicknesses were developed based on the self-assembly of silane molecules on silicon surfaces using N-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA) and octadecyltrichlorosilane (OTS) molecules. Prepared substrates with nano-overlayers were successfully used in the analysis of different types of small target molecules, namely acrivastine, l-histidine, l-valine, l-phenylalanine, l-arginine, l-methionine and angiotensin I. Our substrates exhibited clear peaks almost without fragmentation for all target molecules, suggesting that these surfaces provide a number of important advantages for LDI-MS analysis, such as ease of preparation, costs, reusability, robustness, easy handling and preventing fragmentation.
Graphical Abstract
Graphical abstract Highlights
► A new substrate using controllable nano-structured silicon surfaces based on the self-assembly of silane molecules (OTS and TPDA) was proposed. ► A matrix-free approach for use in laser desorption/ionization mass spectrometry (LDI-MS) for the analysis of small target molecules was demonstrated. ► The modified surfaces with nano-overlayers should be seriously considered to improve LDI-MS analysis. ► The detection of small molecules by eliminating the need for matrix provides a number of important advantages.Dual lifetime referenced fluorometry for the determination of doxorubicin in urine
15 May 2012,
17:58:58
Publication year:
2012
Source:Analytica Chimica Acta, Volume 729
Fernando Martínez Ferreras, Otto S. Wolfbeis, Hans H. Gorris
Dual lifetime referencing (DLR) is introduced as a rapid and self-referenced method for measuring the concentration of a fluorescent analyte in solution. The fluorescent cancer chemotherapeutic doxorubicin was chosen as a medically relevant analyte and blended with a reference dye (Ru(dpp)3) that displays overlapping excitation and emission spectra. The relative contributions of the short-lived (nanoseconds) fluorescent analyte and the long-lived (microseconds) reference dye define the observed lifetime. Measuring this lifetime by both frequency-domain DLR and time-domain DLR yields similar analytical ranges and limits of detection (0.4μM). To assess the matrix effect of medical samples, the standard addition method was employed to both modes of DLR. Urine was spiked with doxorubicin and recovery rates of ≥97% were obtained.
Source:Analytica Chimica Acta, Volume 729
Fernando Martínez Ferreras, Otto S. Wolfbeis, Hans H. Gorris
Dual lifetime referencing (DLR) is introduced as a rapid and self-referenced method for measuring the concentration of a fluorescent analyte in solution. The fluorescent cancer chemotherapeutic doxorubicin was chosen as a medically relevant analyte and blended with a reference dye (Ru(dpp)3) that displays overlapping excitation and emission spectra. The relative contributions of the short-lived (nanoseconds) fluorescent analyte and the long-lived (microseconds) reference dye define the observed lifetime. Measuring this lifetime by both frequency-domain DLR and time-domain DLR yields similar analytical ranges and limits of detection (0.4μM). To assess the matrix effect of medical samples, the standard addition method was employed to both modes of DLR. Urine was spiked with doxorubicin and recovery rates of ≥97% were obtained.
Graphical Abstract
Graphical abstract Highlights
► Self-referenced determination of fluorescent analytes in solution by dual lifetime referencing. ► Comparison of frequency-domain DLR and time-domain DLR. ► DLR has a detection limit of 400nM doxorubicin.Sequence-specific detection of nucleic acids utilizing isothermal enrichment of G-quadruplex DNAzymes
15 May 2012,
17:58:58
Publication year:
2012
Source:Analytica Chimica Acta, Volume 729
Hao-Jie Xiao, Ho Chol Hak, De-Ming Kong, Han-Xi Shen
G-quadruplex DNAzymes are peroxidase-like complexes formed by nucleic acid G-quadruplexes and hemin. Various chemical sensors and biosensors have been developed, based on such DNAzymes. Here we report a novel, specific nucleic acid detection method utilizing the isothermal amplification strategy of G-quadruplex DNAzymes. In this method, an unlabeled oligonucleotide probe was used. The probing sequence of the oligonucleotide was in the form of a stem-loop structure. A G-rich sequence, containing three GGG repeats, was linked to the 5′-end of the stem-loop structure. In the presence of target, the probing sequence hybridized to the target, and a G n (n ≥2) repeat was extended from its 3′-end. This G n repeat, together with the three GGG repeats at the 5′-end, folded into a G-quadruplex, and displayed enhanced peroxidase acitivity upon hemin binding. Utilizing the dynamic binding interaction between the probe and its target, the enrichment of G-quadruplex DNAzymes was achieved. Using this method, simple, rapid and cost-effective nucleic acid detection could be achieved. This method displayed high target-length tolerance and good detection specificity; one-base mismatch could be judged easily, even by visual inspection. This method may be used as an auxiliary tool for amplified detection of specific DNA targets in some situations, in which isothermal detection is desirable.
Source:Analytica Chimica Acta, Volume 729
Hao-Jie Xiao, Ho Chol Hak, De-Ming Kong, Han-Xi Shen
G-quadruplex DNAzymes are peroxidase-like complexes formed by nucleic acid G-quadruplexes and hemin. Various chemical sensors and biosensors have been developed, based on such DNAzymes. Here we report a novel, specific nucleic acid detection method utilizing the isothermal amplification strategy of G-quadruplex DNAzymes. In this method, an unlabeled oligonucleotide probe was used. The probing sequence of the oligonucleotide was in the form of a stem-loop structure. A G-rich sequence, containing three GGG repeats, was linked to the 5′-end of the stem-loop structure. In the presence of target, the probing sequence hybridized to the target, and a G n (n ≥2) repeat was extended from its 3′-end. This G n repeat, together with the three GGG repeats at the 5′-end, folded into a G-quadruplex, and displayed enhanced peroxidase acitivity upon hemin binding. Utilizing the dynamic binding interaction between the probe and its target, the enrichment of G-quadruplex DNAzymes was achieved. Using this method, simple, rapid and cost-effective nucleic acid detection could be achieved. This method displayed high target-length tolerance and good detection specificity; one-base mismatch could be judged easily, even by visual inspection. This method may be used as an auxiliary tool for amplified detection of specific DNA targets in some situations, in which isothermal detection is desirable.
Graphical Abstract
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