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Analytica Chimica Acta (v.741, #)

Editorial Board (pp. iii).

A new application of scanning electrochemical microscopy for the label-free interrogation of antibody–antigen interactions: Part 2 by Joanne L. Holmes; Frank Davis; Stuart D. Collyer; Séamus P.J. Higson (pp. 1-8).
Display Omitted► Employed scanning electrochemical microscopy for label-free detection of antigen binding. ► Demonstrated selective and quantitative binding of three different antigens. ► Detected antigens with a wide range of molecular weights. ► Demonstrated detection of ciprofloxacin in bovine milk.Within this paper we describe the use of scanning electrochemical microscopy (SECM) to fabricate a dotted array of biotinylated polyethyleneimine which was then used to immobilise first neutravidin and then a biotinylated antibody towards a relevant antigen of interest (PSA, NTx, ciprofloxacin). These antigens were selected both for their clinical relevance but also since they display a broad range of molecular weights, to determine whether the size of the antigen used effects the sensitivity of this approach. The SECM was then used to image the binding of both complementary and non-complementary antigens in a label-free assay. Imaging of the arrays before and following exposure to various concentrations of antigen in buffer showed clear evidence for specific binding of the complementary antigens to the antibody functionalised dots. Non-specific binding was also quantified by control experiments with other antigens. This demonstrated non-specific binding across the whole of the substrate, thereby confirming that specific binding does occur between the antibody and antigen of interest at the surface of the dots. The binding of ciprofloxacin was investigated both in simple buffer solution and in a more complex media, bovine milk.

Keywords: Scanning electrochemical microscopy; PSA; NTx; Ciprofloxacin; Label-free; Antibody


Sorbent materials for separation and preconcentration of gold in environmental and geological samples – A review by Krystyna Pyrzynska (pp. 9-14).
Display Omitted► Gold determination requires very often preconcentration and separation. ► Solid phase extraction technique offers for this purpose high enrichment factor, rapid phase separation and the ability of combination with different detection techniques. ► The recent developments in this area were presented and discussed.Determination of gold in environmental and geological samples requires very often preconcentration and separation due to the high concentration of interfering matrix components and the low content of this metal. Solid phase extraction technique with different kind of solid sorbents offers for this purpose high enrichment factor, rapid phase separation and the ability of combination with different detection techniques. It can be easily implemented and controlled in flow systems, The recent developments in this area are presented and discussed.

Keywords: Gold; Solid sorbents; Enrichment; Separation


Simultaneous determination of ascorbic acid, dopamine, uric acid and tryptophan on gold nanoparticles/overoxidized-polyimidazole composite modified glassy carbon electrode by Cun Wang; Ruo Yuan; Yaqin Chai; Shihong Chen; Fangxin Hu; Meihe Zhang (pp. 15-20).
Electropolymerization of Im on the GCE, the PIm modified electrode was denoted as PIm/GCE. Subsequently, the PIm/GCE was washed with doubly distilled water, and then transferred to 0.1M PBS (pH 4.0) for electrochemical oxidation at +1.8V for 250s. The obtained electrode was denoted as PImox/GCE (Fig. A). Then, the deposition of GNPs on PImox/GCE was carried out. The obtained electrode was described as GNPs/PImox/GCE (Fig. B).Display Omitted► The electropolymerization of imidazole (Im) on GCE was first reported. ► The PIm film can be overoxidized to form the overoxidized polyimidazole (PImox). ► PImox allows dispersing of Au and generates additional electrocatalytic sites. ► The overlapping voltammetric response of AA, DA, UA and Trp is well-resolved.A novel electrode was developed through electrodepositing gold nanoparticles (GNPs) on overoxidized-polyimidazole (PImox) film modified glassy carbon electrode (GCE). The combination of GNPs and the PImox film endowed the GNPs/PImox/GCE with good biological compatibility, high selectivity and sensitivity and excellent electrochemical catalytic activities towards ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp). In the fourfold co-existence system, the peak separations between AA–DA, DA–UA and UA–Trp were large up to 186, 165 and 285mV, respectively. The calibration curves for AA, DA and UA were obtained in the range of 210.0–1010.0μM, 5.0–268.0μM and 6.0–486.0μM with detection limits (S/N=3) of 2.0μM, 0.08μM and 0.5μM, respectively. Two linear calibrations for Trp were obtained over ranges of 3.0–34.0μM and 84.0–464.0μM with detection limit (S/N=3) of 0.7μM. In addition, the modified electrode was applied to detect AA, DA, UA and Trp in samples using standard addition method with satisfactory results.

Keywords: Imidazole; Gold nanoparticles; Ascorbic acid; Dopamine; Uric acid; Tryptophan


A highly accurate method for determination of dissolved oxygen: Gravimetric Winkler method by Irja Helm; Lauri Jalukse; Ivo Leito (pp. 21-31).
Display Omitted► Probably the most accurate method available for dissolved oxygen concentration measurement was developed. ► Careful analysis of uncertainty sources was carried out and the method was optimized for minimizing all uncertainty sources as far as practical. ► This development enables more accurate calibration of dissolved oxygen sensors for routine analysis than has been possible before.A high-accuracy Winkler titration method has been developed for determination of dissolved oxygen concentration. Careful analysis of uncertainty sources relevant to the Winkler method was carried out and the method was optimized for minimizing all uncertainty sources as far as practical. The most important improvements were: gravimetric measurement of all solutions, pre-titration to minimize the effect of iodine volatilization, accurate amperometric end point detection and careful accounting for dissolved oxygen in the reagents. As a result, the developed method is possibly the most accurate method of determination of dissolved oxygen available. Depending on measurement conditions and on the dissolved oxygen concentration the combined standard uncertainties of the method are in the range of 0.012–0.018mgdm−3 corresponding to the k=2 expanded uncertainty in the range of 0.023–0.035mgdm−3 (0.27–0.38%, relative). This development enables more accurate calibration of electrochemical and optical dissolved oxygen sensors for routine analysis than has been possible before.

Keywords: Dissolved oxygen; Winkler method; Uncertainty; Primary method


Sensitive and robotic determination of bromate in sea water and drinking deep-sea water by headspace solid-phase micro extraction and gas chromatography–mass spectrometry by Hyun-Hee Lim; Ho-Sang Shin (pp. 32-37).
Display Omitted► This study is the first analysis method with HS SPME GC–MS of bromate. ► Selection of reagent and fibre, reaction temperature/time and pH were optimized. ► The best reagent and fiber is 2,6-DMP and CAR-PDMS. ► LOD and LOQ in sea water were 0.016 and 0.051μgL−1 and RSD was less than 7.0%.A robotic method has been established for the determination of bromate in sea water and drinking deep-sea water. Bromate in water was converted into volatile derivative, which was measured with headspace solid-phase micro extraction and gas chromatography–mass spectrometry (HS-SPME GC–MS). Derivatization reagent and the HS-SPME parameters (selection of fibre, extraction/derivatization temperature, heating time and; the morality of HCl) were optimized and selected. Under the established conditions, the detection and the quantification limits were 0.016μgL−1 and 0.051μgL−1, respectively, and the intra- and inter-day relative standard deviation was less than 7% at concentrations of 1.0 and 10.0μgL−1. The calibration curve showed good linearity with r2=0.9998. The common ions Cl−, NO3−, SO42−, HPO42−, H2PO4−, K+, Na+, NH4+, Ca2+, Mg2+, Ba2+, Mn4+, Mn2+, Fe3+ and Fe2+ did not interfere even when present in 1000-fold excess over the active species. The method was successfully applied to the determination of bromate in sea water and drinking deep-sea water.

Keywords: Bromate; Headspace solid-phase microextraction; Gas chromatography–mass spectrometry; Sea water


Membrane-based microchannel device for continuous quantitative extraction of dissolved free sulfide from water and from oil by Kei Toda; Yuki Ebisu; Kazutoshi Hirota; Shin-Ichi Ohira (pp. 38-46).
Display Omitted► We have developed a membrane-based microchannel extraction (HMCE) device. ► Extraction efficiency was examined theoretically and experimentally for this device. ► Quantitative extraction can be performed with the HMCE device while partial extraction with other conventional membrane-based devices. ► The HMCE device was applied for the measurement of free sulfide or hydrogen sulfide contained in water and oil samples. ► The presented device is expected to be used for survey of underground fluid such as groundwater and oil in future.Underground fluids are important natural sources of drinking water, geothermal energy, and oil-based fuels. To facilitate the surveying of such underground fluids, a novel microchannel extraction device was investigated for in-line continuous analysis and flow injection analysis of sulfide levels in water and in oil. Of the four designs investigated, the honeycomb-patterned microchannel extraction (HMCE) device was found to offer the most effective liquid–liquid extraction. In the HMCE device, a thin silicone membrane was sandwiched between two polydimethylsiloxane plates in which honeycomb-patterned microchannels had been fabricated. The identical patterns on the two plates were accurately aligned. The extracted sulfide was detected by quenching monitoring of fluorescein mercuric acetate (FMA). The sulfide extraction efficiencies from water and oil samples of the HMCE device and of three other designs (two annular and one rectangular channel) were examined theoretically and experimentally. The best performance was obtained with the HMCE device because of its thin sample layer (small diffusion distance) and large interface area. Quantitative extraction from both water and oil could be obtained using the HMCE device. The estimated limit of detection for continuous monitoring was 0.05μM, and sulfide concentrations in the range of 0.15–10μM could be determined when the acceptor was 5μM FMA alkaline solution. The method was applied to natural water analysis using flow injection mode, and the data agreed with those obtained using headspace gas chromatography-flame photometric detection. The analysis of hydrogen sulfide levels in prepared oil samples was also performed. The proposed device is expected to be used for real time survey of oil wells and groundwater wells.

Keywords: Liquid–liquid extraction; Honeycomb-patterned microchannel extraction device; Continuous and quantitative extraction of dissolved free sulfide from water and hydrogen sulfide from oil; Underground fluids


Silica nanoparticles pre-spotted onto target plate for laser desorption/ionization mass spectrometry analyses of peptides by Mathieu Dupré; Sonia Cantel; Jean-Olivier Durand; Jean Martinez; Christine Enjalbal (pp. 47-57).
Display Omitted► We present a new pre-spotted MALDI target for peptide detection and sequencing. ► The inert substrate consists of silica nanoparticles easily prepared by sol–gel chemistry. ► This very efficient LDI-promoting support produces ions from few femtomoles of mixtures of peptides. ► Rapid MS profiling and subsequent MS/MS analyses are achieved.We report on the simple deposition of Stöber silica nanoparticles (SiO2 NPs) on conventional MALDI target plate for high throughput laser desorption/ionization mass spectrometry (LDI-MS) analyses of peptide mixtures with sensitivity in the femtomolar range. This low-cost easily prepared material allowed straightforward LDI experiments by deposition of the studied samples directly onto a pre-spotted MALDI plate. This analytical strategy can be performed in any laboratory equipped with a MALDI-TOF instrument. All key benefits of organic matrix-free technologies were satisfied while maintaining a high level of detection performances (sensitivity and reproducibility/repeatability). In particular, sample preparation was simple and detection in the low mass range was not hampered by matrix ions. Imaging studies were undertaken to query sample dispersion into the inert SiO2 NPs and to help into the search of the best experimental conditions producing homogeneous analyte distribution within the deposit. In contrast to commercial disposable LDI targets designed for single use and requiring an adaptor such as NALDI™, the proposed SiO2 NPs pre-spotting on a MALDI target plate allowed very easily switching between MALDI and LDI experiments. They can be conducted either simultaneously (positions with an organic matrix or SiO2 NPs) or in the row (support prepared in advance, stored and washed after use). The overall cost and versatility of the methodology made it very attractive to MALDI users in many domains (peptidomics, proteomics, metabolomics).

Keywords: Peptide; LDI-MS; SALDI-MS; Matrix-free; Silica nanoparticles; Pre-spotted target


A direct assessment of mycotoxin biomarkers in human urine samples by liquid chromatography tandem mass spectrometry by Emmanuel Njumbe Ediage; Jose Diana Di Mavungu; Suquan Song; Aibo Wu; Carlos Van Peteghem; Sarah De Saeger (pp. 58-69).
Display Omitted► The method was established for analysis of mycotoxin biomarkers in human urine. ► LLE with acidified ethyl acetate was very efficient as extraction solvent. ► Direct determination of the glucuronides was performed without enzyme digestion. ► Optimization of the analytical parameters was achieved with a D-optimal design. ► The proposed sample preparation method is simple, cheaper and robust.Detection of mycotoxin biomarkers in urine of humans and animals provides a direct approach for assessing exposure to these mycotoxins as opposed to the indirect approach of food analysis, which in most cases is affected by the heterogeneity of the toxin in the food samples. Seven (7) mycotoxins and their metabolites (total 18 analytes) were selected and an LC–MS/MS method for their determination in human urine was developed and validated. The method consisted of direct analysis of two mycotoxin conjugates, deoxynivalenol-glucuronide and zearalenone-glucuronide without beta glucuronidase digestion of the urine samples. Since high method sensitivity is of utmost importance in such study, critical factors which could improve the analyte recovery and method sensitivity were investigated by a D-optimal experimental design. Urine samples (10mL) were first extracted with 15mL ethyl acetate/formic acid (99/1, v/v) followed by SAX SPE clean-up of the acidified aqueous fraction. Both extracts were combined and analyzed using an LC–MS/MS system operated in the positive ionization mode. A total run time of 28min was adopted with all the 18 analytes eluting within 15min.The method was validated by taking into consideration the guidelines specified in Commission Decision 2002/657/EC and 401/2006/EC. Forty samples obtained from volunteers within the laboratory research group were analyzed as part of a pilot study. All results were expressed per mg creatinine. A total of 9 samples were found contaminated with one or more of the following analytes: DON, OTA, OTα, 4-OH OTA, ZEN, CIT and β-ZOL. One-eighth (5/40) of the samples were contaminated with DON in the range of 3.7–67ngmg−1 creatinine. Samples with detectable levels of DON did not show any co-occurrence of DON-3Glu. One sample was found to be contaminated with 4-OH OTA (−1 creatinine). OTα (up to 4.4ngmg−1 creatinine) was detected in three other samples co-occurring with low levels of OTA (up to 0.3ngmg−1 creatinine) and no 4-OH OTA detected. ZEN was detected in 10% (4/40) of the samples analyzed. Three samples were contaminated with β-ZOL (3.3–20ngmg−1 creatinine), co-occurring with ZEN (−1 creatinine). The ratio of ZEN/β-ZOL varied for all the three samples. α-ZOL was not detected in any of the 40 samples. CIT was detected in one sample at 4.5ngmg−1 creatinine. This is the first study carried out with a small group of the Belgian population to assess exposure to mycotoxins using biomarkers.

Keywords: Mycotoxin; Biomarkers; Urine; Glucuronide; Experimental design; Stability study


Sample handling and contamination encountered when coupling offline normal phase high performance liquid chromatography fraction collection of petroleum samples to Fourier transform ion cyclotron resonance mass spectrometry by Nicole E. Oro; Randy M. Whittal; Charles A. Lucy (pp. 70-77).
Display Omitted► We collect HPLC fractions of gas oils offline for FT-ICR MS analysis. ► Optimized sample preparation procedures are described. ► MS contamination encountered is described and eliminated. ► Three new contaminants are identified, including iron-formate clusters.Normal phase high performance liquid chromatography (HPLC) is used to separate a gas oil petroleum sample, and the fractions are collected offline and analyzed on a high resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR MS). The separation prior to MS analysis dilutes the sample significantly; therefore the fractions need to be prepared properly to achieve the best signal possible. The methods used to prepare the HPLC fractions for MS analysis are described, with emphasis placed on increasing the concentration of analyte species. The dilution effect also means that contamination in the MS spectra needs to be minimized. The contamination from molecular sieves, plastics, soap, etc. and interferences encountered during the offline fraction collection process are described and eliminated. A previously unreported MS contamination of iron formate clusters with a 0.8 mass defect in positive mode electrospray is also described. This interference resulted from the stainless steel tubing in the HPLC system. Contamination resulting from what has tentatively been assigned as palmitoylglycerol and stearoylglycerol was also observed; these compounds have not previously been reported as contaminant peaks.

Keywords: Offline fraction collection; HPLC; Mass spectrometry; Petroleomics; Contamination


Analysis of steroids in human urine by on line liquid chromatography–gas chromatography–mass spectrometry using the Through Oven Transfer Adsorption Desorption interface and a fraction collector by Rosa M. Toledano; Eva M. Díaz-Plaza; José M. Cortés; Inmaculada Blázquez; Ana Vázquez; Jesús Villén; Jesús Muñoz-Guerra (pp. 78-85).
Display Omitted► A new method to analyze steroids in human urine by LC–GC–MS has been developed. ► The TOTAD interface with a fraction collector is used in the on line coupling LC–GC. ► A newly designed fraction collector, totally automated, is described for the first time. ► Different LC fractions were analyzed in a sole injection of sample. ► The sensitivity achieved permits the detection limits set by WADA to be attained.Anti-doping laboratories accredited by the WADA (World Anti-Doping Agency) must have available methods capable of detecting synthetic steroids at concentrations below 10ngmL−1 and, at the same time, be able to quantify endogenous steroids with accuracy. The unequivocal identification of the steroids must be carried out by GC–MS. In this manuscript we describe a new method by on-line coupled liquid chromatography–gas chromatography (LC–GC) using the Through Oven Transfer Adsorption Desorption (TOTAD) interface and mass spectrometer (MS) detector. By this means, all the analyte eluted in the LC stage are automatically transferred to the GC, avoiding the contamination associated with manipulation of the sample. A newly designed fraction collector is described for the first time. The collector permits the different fractions eluted in LC to be stored and sent individually to the GC by means of the TOTAD interface. The detection limits attained, measured in gas chromatography–mass spectrometry (GC–MS) in SCAN mode, vary between 0.5 and 3.4ngmL−1, and the method, once the sample is derivatized, is completely automatic.

Keywords: On line coupled liquid chromatography–gas chromatography–mass spectrometry; Through Oven Transfer Adsorption Desorption interface with fraction collector; Steroid analysis; Doping; Human urine; Natural steroids


Characterization of CdTe/CdSe quantum dots-transferrin fluorescent probes for cellular labeling by Li-Yun Guan; Yong-Qiang Li; Song Lin; Ming-Zhen Zhang; Jun Chen; Zhi-Ya Ma; Yuan-Di Zhao (pp. 86-92).
Display Omitted► A convenient method was designed to assess cell efficiency of QDs probes for cellular labeling. ► The relationship between conjugation methods and effectiveness was evaluated clearly. ► QDs-Tf probe synthesized by EDC coupling had the highest labeling efficiency, followed by electrostatic interaction, and dTf coating.In this paper, we prepared three types of transferrin-quantum dots conjugates (QDs-Tf) using three different methods (electrostatic interaction, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) coupling, denatured transferrin (dTf) coating). Fluorescence emission spectra, surface characteristics, zeta potentials of quantum dots (QDs) and QDs-Tf fluorescent probes were characterized by spectrophotometer, capillary electrophoresis, and dynamic light scattering. Fluorescent imaging of HeLa cells was also performed by QDs and QDs-Tf fluorescent probes. It was found that the fluorescence imaging performances of QDs-Tf probes prepared by electrostatic interaction and EDC coupling were better compared with the one prepared by dTf coating. Then a real-time single cell detection system was established to quantitatively evaluate cell labeling effects of QDs-Tf fluorescent probes. It was found that for cell labeling efficiency, the proportion of cells labeled by quantum dot probes to a group of cells, QDs-Tf probe prepared by EDC coupling showed the highest labeling efficiency (85.55±3.88%), followed by electrostatic interaction (78.86±9.57%), and dTf coating showed the lowest (40.09±10.2%). This efficiency order was confirmed by flow cytometry results. This study demonstrated the relationship between conjugation methods and the resultant QDs-Tf probes and provided a foundation for choosing appropriate QDs-Tf probes in cell labeling.

Keywords: Quantum dots; Transferrin; Conjugation methods; Cellular labeling; Labeling efficiency


In situ labeling and imaging of cellular protein via a bi-functional anticancer aptamer and its fluorescent ligand by Jun Ai; Tao Li; Bingling Li; Yuanhong Xu; Dan Li; Zuojia Liu; Erkang Wang (pp. 93-99).
In this work, we report a novel approach to in situ labeling and imaging of a cellular protein nucleolin utilizing a multifunctional anticancer aptamer combined with its fluorescent ligand.Display Omitted► AS1411 bind protoporphyrin IX and enhances the fluorescence signal remarkably. ► According to LSCM experiment, HeLa cells were imagined by AS1411–PPIX. ► Aptamer-based bioimaging plays an important role for need not any covalent modification.In this article, we reported a novel approach for in situ labeling and imaging HeLa cancer cells utilizing a bifunctional aptamer (AS1411) and its fluorescent ligand, protoporphyrin IX (PPIX). In the presence of potassium ion, AS1411 folded to G-quadruplex structure, binded fluorescent ligand (PPIX) with fluorescent enhancement, and targeted the nucleolin overexpressed by cancer cells. Consequently, bioimaging of cancer cells specifically were realized by laser scanning confocal microscope. The bioimaging strategy with AS1411–PPIX complex was capable to distinguish HeLa cancer cells from normal cells unambiguously, and fluorescence imaging of cancer cells was also realized in human serum. Moreover, the bioimaging method was very facile, effective and need not any covalent modification. These results illustrated that the useful approach can provide a novel clue for bioimaging based on non-covalent bifunctional aptamer in clinic diagnosis.

Keywords: AS1411; Nucleolin; HeLa cells; Fluorescence; Bioimaging


Quantum-dot-based homogeneous time-resolved fluoroimmunoassay of alpha-fetoprotein by Mei-Jun Chen; Ying-Song Wu; Guan-Feng Lin; Jing-Yuan Hou; Ming Li; Tian-Cai Liu (pp. 100-105).
Display Omitted► QDs-based homogeneous time-resolved fluoroimmunoassay was developed to detect AFP. ► The conjugates were prepared with QDs-doped microspheres and anti-AFP McAb. ► The conjugates were prepared with LTCs and another anti-AFP McAb. ► Excess amounts of conjugates were used for detecting AFP without rinsing. ► The wedding of QPs and LTCs was suitable for HTRFIA to detect AFP.Quantum dots (QDs) with novel photoproperties are not widely used in clinic diagnosis, and homogeneous time-resolved fluorescence assays possess many advantages over current methods for alpha-fetoprotein (AFP) detection. A novel QD-based homogeneous time-resolved fluorescence assay was developed and used for detection of AFP, a primary marker for many cancers and diseases. QD-doped carboxyl-modified polystyrene microparticles (QPs) were prepared by doping oil-soluble QDs possessing a 605nm emission peak. The antibody conjugates (QPs-E014) were prepared from QPs and an anti-AFP monoclonal antibody, and luminescent terbium chelates (LTCs) were prepared and conjugated to a second anti-AFP monoclonal antibody (LTCs-E010). In a double-antibodies sandwich structure, QPs-E014 and LTCs-E010 were used for detection of AFP, serving as energy acceptor and donor, respectively, with an AFP bridge. The results demonstrated that the luminescence lifetime of these QPs was sufficiently long for use in a time-resolved fluoroassay, with the efficiency of time-resolved Förster resonance transfer (TR-FRET) at 67.3% and the spatial distance of the donor to acceptor calculated to be 66.1Å. Signals from TR-FRET were found to be proportional to AFP concentrations. The resulting standard curve was log Y=3.65786+0.43863·log X ( R=0.996) with Y the QPs fluorescence intensity and X the AFP concentration; the calculated sensitivity was 0.4ngmL−1. By assaying test samples against the standard curve, the coefficient of variations was <5%, indicating that QDs were suitable for this homogenous time-resolved fluoroimmunoassay. This work extended the potential applications of QDs in future homogeneous analytical bioassays. In the coming research, hepatitis B surface antigen, another primary marker for hepatocellular carcinoma, will be studied for practical detection using a QD-based homogenous multiplex fluoroimmunoassay.

Keywords: Quantum dots; Homogeneous fluoroimmunoassay; FRET; Luminescent terbium complex; Alpha-fetoprotein


A simple colorimetric pH alarm constructed from DNA–gold nanoparticles by Bin Zheng; Sheng Cheng; Wei Liu; Michael Hon-Wah Lam; Haojun Liang (pp. 106-113).
Display Omitted► It is the first time that poly (dA) ssDNAs have been attempted in pH sensing. ► The system can provide very sharp, naked-eyes detectable colorimetric responses upon a specific media pH. ► The approach is simple and detection threshold can be modulated.Because of their unique characteristics, DNAs have been widely studied for uses in biosensors. In this work, we utilize single-stranded homopolymeric deoxyadenosines (abbreviated as poly (dA)) as recognition elements and gold nanoparticles (abbreviated as AuNPs) as reporter parts for the construction of pH alarms, which are able to produce sharp colorimetric responses upon specific pH thresholds within the range from pH 2 to 4. These biosensors are convenient to prepare and easy to operate. Their pH thresholds for colorimetric response can be easily tuned by changes of DNA strand length, concentration and DNA sequence. With an increase in the number of nucleotide bases per DNA chain while keeping the overall number of nucleotide base in the system constant, the pH threshold can be raised. Increasing the concentration of the single-stranded poly (dA) DNA lowers the pH response threshold. Moreover, as they can sense a range as narrow as a 0.4 pH unit which equals to 2.5 fold [H+] change, they can be used as a potential pH alarm for specific pH range.

Keywords: DNA; pH alarm; Gold nanoparticle; Biosensor; Colorimetric
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