Anna-Maria Spehar | Queen Mary, University of London (original) (raw)

Papers by Anna-Maria Spehar

Electrochimica Acta, Mar 1, 2006

Rhodamine B (RhB) exhibits strong cathodic electrogenerated chemiluminescence (ECL) in aqueous so... more Rhodamine B (RhB) exhibits strong cathodic electrogenerated chemiluminescence (ECL) in aqueous solutions during high-amplitude pulse polarization at thin oxide film-coated aluminum electrodes. This method allows the detection of RhB below nanomolar concentration level and provides linear calibration plots spanning over several orders of magnitude of concentration. In addition, a relatively long ECL lifetime of RhB provides a basis for time-resolved detection. Thus, widely used RhB-based labels can also be suggested to be usable as electrochemiluminescent labels in fully aqueous solutions in bioaffinity assays such as in immunoassays and DNA-probing assays. Support was obtained for the chemiluminescence generation mechanism to be essentially the same as that of radiochemiluminescence in aqueous solution.

Food Chemistry, Function and Analysis, 2019

In this chapter, we focus on label-free techniques suitable for the detection of analytes in food... more In this chapter, we focus on label-free techniques suitable for the detection of analytes in food samples. We demonstrate the capabilities of such techniques on optics-based (surface plasmon resonance, SPR) and acoustic-based (quartz crystal microbalance, QCM) devices using immunoassays. Label-free techniques can be miniaturised and thus can be brought closer to the point of use, such as a farm, a field, a storage space, a shipyard, a factory gate or even a restaurant. First, the working principles of traditional SPR and of a QCM are introduced. The basic terminology is briefly covered and common technical considerations, including the required surface chemistry, limit of detection, ability to multiplex, ability to work with crude samples and complexity of liquid handling, are discussed. Secondly, commercial instruments are described including Biacore, ForteBio and Q-Sense. In addition, newer technical variations such as fibre-optic SPR (FOX diagnostics), imaging SPR (Horiba), multi...

2013 IEEE International Conference on Body Sensor Networks, 2013

To enable continuous monitor ing of electr ochemical sensor s outside the labor ator ies, ther e ... more To enable continuous monitor ing of electr ochemical sensor s outside the labor ator ies, ther e is a significant demand on electr ochemical measur ement systems to be miniatur ized. The paper pr esents a low-cost, por table miniatur e device for electr ochemical measur ements. The device consists of a 35mm x 20mm x 25mm wir eless tag, which enables potentiometr ic and amper ometr ic measur ement, and a base station for data acquisition. Potentiometr ic per for mance is evaluated using solid contact ion selective electr odes for pH and sodium. High sensitivity, r epeatability and fast r esponse time have been achieved. Amper ometr ic measur ement of hydr ogen per oxide shows that the measur ed cur r ent accur acy and sensitivity ar e compar able to that of a commer cial potentiostat. M or eover , the device can be used for lactate concentr ation sensing.

2012 Ninth International Conference on Wearable and Implantable Body Sensor Networks, 2012

Lactate is one of the most important biomarkers of tissue oxygenation and thus of paramount impor... more Lactate is one of the most important biomarkers of tissue oxygenation and thus of paramount importance for sports and health care applications. Lactate levels provide information on anaerobic threshold which is very important for tailoring training programs in endurance sports. In this contribution we present an implantable amperometric lactate sensor for continuous in vivo monitoring. A needle based construction is

NATO Science for Peace and Security Series A: Chemistry and Biology, 2012

Essential properties of biosensors for continuous monitoring in blood and tissue are selectivity,... more Essential properties of biosensors for continuous monitoring in blood and tissue are selectivity, sensitivity and biocompatibility. A variety of membranes have been explored to achieve these properties. A good understanding of the diffusion properties of analytes and ...

Journal of Luminescence, 2006

Reactive Al/OH−(aq) interface was studied and used as a source of chemical energy in the generati... more Reactive Al/OH−(aq) interface was studied and used as a source of chemical energy in the generation of chemiluminescence. The observed extrinsic lyoluminescence emission during dissolution of aluminum in an alkaline Tb (III) or Eu (III) chelate solution was clearly based ...

Electroanalysis, 2013

ABSTRACT The properties of electropolymerised phenolic films at amperometric needle electrodes we... more ABSTRACT The properties of electropolymerised phenolic films at amperometric needle electrodes were investigated and their applicability as selective, internal barriers for potential in vivo oxidase enzyme based biosensors evaluated. Polyphenol, poly(phenol red) and dual layer poly(phenol red)/poly(4-aminophenol) films were formed by electropolymerisation and compared with a solvent deposited sulfonated polyether ether sulfonepolyether sulfone (SPEES-PES) membrane. Phenol red had two distinct cyclic voltammetry peaks on platinum: an oxidative peak at +0.70 V and a reduction peak at −0.2 V vs. Ag/AgCl, respectively. Also, the film enhanced the oxidation of hydrogen peroxide by a factor of 3–4, making it an attractive barrier for oxidase based biosensors. Lactate sensors made with polyphenolic electropolymers and solvent deposited SPEES/PES were compared for selectivity and lactate response; the latter showed better selectivity against acetaminophen but less selectivity against ascorbic acid. When sensors were sterilised by standard gamma – irradiation for in vivo application, the polyphenolic films degraded and lost selectivity, whilst SPEES/PES survived unchanged. Salivary lactate was monitored during exercise with electropolymerised film sensors and demonstrated mean lactate increases of 0.3–0.6 mM.

Analytica Chimica Acta, 2002

Cathodic pulse polarisation of oxide-covered aluminium electrodes can generate electrochemilumine... more Cathodic pulse polarisation of oxide-covered aluminium electrodes can generate electrochemiluminescence (ECL) from metalloporphyrins. This is based on the tunnel emission of hot electrons into aqueous electrolyte solution, which probably results in the generation of hydrated electrons as reducing mediators. These tunnel emitted electrons allow the production of highly reactive radicals, such as sulfate radicals from peroxodisulfate ions, which can induce strong redox luminescence from various organic chemiluminophores including metalloporphyrins. The work presented here illustrates the generation of ECL from platinum(II) coproporphyrin (PtCP) and its bovine serum albumin (BSA) conjugate. This allows the detection of these molecules below nanomolar concentrations and over several orders of magnitude of concentration. The relatively long luminescence lifetime of PtCP allows discrimination from the background ECL signal using time resolved measurements, leading to higher sensitivity and the detection of PtCP-BSA indicates the potential use of metalloporphyrins as labels in ECL-based bioassays such as immunoassays and DNA-binding assays.

Analytica Chimica Acta, 2005

Cathodic DC polarization of oxide-covered aluminum produces electrogenerated chemiluminescence fr... more Cathodic DC polarization of oxide-covered aluminum produces electrogenerated chemiluminescence from hydrated and chelated Tb(III) ions in aqueous electrolyte solutions. At the moment of cathodic voltage onset, a strong cathodic flash is observed, which is attributed to a tunnel emission of hot electrons into the aqueous electrolyte solution and the successive chemical reactions with the luminophores. However, within a few milliseconds the insulating oxide film is damaged and finally dissolved due to (i) indiffusion of protons or alkali metal ions into the thin oxide film, (ii) subsequent hydrogen evolution at the aluminum/oxide interface and (iii) alkalization of the electrode surface induced by hydrogen evolution reaction. When the alkalization of the electrode surface has proceeded sufficiently, chemiluminescence is generated with increasing intensity. Aluminum metal, short-lived Al(II), Al(I) or atomic hydrogen and its conjugated base form, hydrated electron, can act as highly reducing species in addition to the less energetic heterogeneously transferred electrons from the aluminum electrode. Tb(III) added as a hydrated ion in the solution probably luminesces in the form of Tb(OH) 3 or Tb(OH) 4 − by direct redox reactions of the central ion whereas multidentate aromatic ligand chelated Tb(III) probably luminesces by ligand sensitized chemiluminescence mechanism in which ligand is first excited by one-electron redox reactions, which is followed by intramolecular energy transfer to the central ion which finally emits light.

Analytica Chimica Acta, 2006

Time-resolved electrogenerated chemiluminescence of multidentate phenolic Eu(III) chelates were s... more Time-resolved electrogenerated chemiluminescence of multidentate phenolic Eu(III) chelates were studied in aqueous solution. 2,6-bis[N,Nbis(carboxymethyl)-aminomethyl]-4-benzoylphenol forms a photoluminescent and electrochemiluminescent Eu(III) chelate, whereas 2,6-bis[N,Nbis(carboxymethyl)-aminomethyl]-4-methyl phenol-chelated Eu(III) turned out to be not luminescent at all. The importance of the redox properties of both the ground and the excited states of the ligands and the central ion is shown. The former chelate shows relatively weak ECL at an oxidecovered aluminum electrode but the ECL intensity can be strongly enhanced by the addition of peroxodisulfate ions. In the presence of 1 mM peroxodisulfate ions the ECL lifetime of this chelate is 0.94 ms, thus easily allowing time-resolved detection of the chelate. This chelate can be conjugated to antibodies by thioureido linkage and used as an electrochemiluminescent label in immunoassays as a marker which displays long-lived luminescence in the red end of the optical spectrum. The present ECL is mainly based on the ligand sensitized redox excitation of the chelate by analogous pathways to those known from the studies of aromatic Tb(III) chelates but the energy transfer from the emission centers of the aluminum oxide film can also have minor contribution to the excitation of the label.

Analytica Chimica Acta, 2002

ABSTRACT Heterogeneous and homogeneous immunoassays of human thyroid stimulating hormone (hTSH) w... more ABSTRACT Heterogeneous and homogeneous immunoassays of human thyroid stimulating hormone (hTSH) were developed on immunometric basis using aromatic Tb(III) chelates as electrochemiluminescent labels and varied types of disposable oxide-covered aluminum electrodes as the solid phase of the immunoassays. The long luminescence lifetime of the present labels allows the use of time-resolved electrochemiluminescence detection and provide the low detection limits of these labels and, thus, sensitive immunoassays. The primary antibody of immunometric immunoassays was coated upon aluminum oxide surface by physical absorption. In homogeneous immunoassays using 66 μl cell and 15 min incubation time, a linear calibration range of 0.25–324 μU/ml was obtained by applying only a single cathodic excitation pulse in the detection step of the assay.

Analytica Chimica Acta, 2002

Hot electrons can be injected from conductor/insulator/electrolyte (C/I/E) junctions into an aque... more Hot electrons can be injected from conductor/insulator/electrolyte (C/I/E) junctions into an aqueous electrolyte solution. Injected hot electrons induce electrogenerated chemiluminescence (ECL) of various luminophores in fully aqueous solutions. Such ECL gives the basis of electrochemiluminoimmunoassays and DNA-probe assays where different luminophores can be used as electrochemiluminescent labels. This work shows that SYBR ® Green I is suitable as an ECL label in detection methods based on C/I/E tunnel-emission electrodes such as oxide-coated aluminium, magnesium and silicon electrodes.

To enable continuous monitoring of electrochemical sensors outside the laboratories, there is a s... more To enable continuous monitoring of
electrochemical sensors outside the laboratories, there is a
significant demand on electrochemical measurement systems to
be miniaturized. The paper presents a low-cost, portable
miniature device for electrochemical measurements. The device
consists of a 35mm x 20mm x 25mm wireless tag, which enables
potentiometric and amperometric measurement, and a base
station for data acquisition. Potentiometric performance is
evaluated using solid contact ion selective electrodes for pH and
sodium. High sensitivity, repeatability and fast response time
have been achieved. Amperometric measurement of hydrogen
peroxide shows that the measured current accuracy and
sensitivity are comparable to that of a commercial potentiostat.
Moreover, the device can be used for lactate concentration
sensing.

Electrochimica Acta, Mar 1, 2006

Rhodamine B (RhB) exhibits strong cathodic electrogenerated chemiluminescence (ECL) in aqueous so... more Rhodamine B (RhB) exhibits strong cathodic electrogenerated chemiluminescence (ECL) in aqueous solutions during high-amplitude pulse polarization at thin oxide film-coated aluminum electrodes. This method allows the detection of RhB below nanomolar concentration level and provides linear calibration plots spanning over several orders of magnitude of concentration. In addition, a relatively long ECL lifetime of RhB provides a basis for time-resolved detection. Thus, widely used RhB-based labels can also be suggested to be usable as electrochemiluminescent labels in fully aqueous solutions in bioaffinity assays such as in immunoassays and DNA-probing assays. Support was obtained for the chemiluminescence generation mechanism to be essentially the same as that of radiochemiluminescence in aqueous solution.

Food Chemistry, Function and Analysis, 2019

In this chapter, we focus on label-free techniques suitable for the detection of analytes in food... more In this chapter, we focus on label-free techniques suitable for the detection of analytes in food samples. We demonstrate the capabilities of such techniques on optics-based (surface plasmon resonance, SPR) and acoustic-based (quartz crystal microbalance, QCM) devices using immunoassays. Label-free techniques can be miniaturised and thus can be brought closer to the point of use, such as a farm, a field, a storage space, a shipyard, a factory gate or even a restaurant. First, the working principles of traditional SPR and of a QCM are introduced. The basic terminology is briefly covered and common technical considerations, including the required surface chemistry, limit of detection, ability to multiplex, ability to work with crude samples and complexity of liquid handling, are discussed. Secondly, commercial instruments are described including Biacore, ForteBio and Q-Sense. In addition, newer technical variations such as fibre-optic SPR (FOX diagnostics), imaging SPR (Horiba), multi...

2013 IEEE International Conference on Body Sensor Networks, 2013

To enable continuous monitor ing of electr ochemical sensor s outside the labor ator ies, ther e ... more To enable continuous monitor ing of electr ochemical sensor s outside the labor ator ies, ther e is a significant demand on electr ochemical measur ement systems to be miniatur ized. The paper pr esents a low-cost, por table miniatur e device for electr ochemical measur ements. The device consists of a 35mm x 20mm x 25mm wir eless tag, which enables potentiometr ic and amper ometr ic measur ement, and a base station for data acquisition. Potentiometr ic per for mance is evaluated using solid contact ion selective electr odes for pH and sodium. High sensitivity, r epeatability and fast r esponse time have been achieved. Amper ometr ic measur ement of hydr ogen per oxide shows that the measur ed cur r ent accur acy and sensitivity ar e compar able to that of a commer cial potentiostat. M or eover , the device can be used for lactate concentr ation sensing.

2012 Ninth International Conference on Wearable and Implantable Body Sensor Networks, 2012

Lactate is one of the most important biomarkers of tissue oxygenation and thus of paramount impor... more Lactate is one of the most important biomarkers of tissue oxygenation and thus of paramount importance for sports and health care applications. Lactate levels provide information on anaerobic threshold which is very important for tailoring training programs in endurance sports. In this contribution we present an implantable amperometric lactate sensor for continuous in vivo monitoring. A needle based construction is

NATO Science for Peace and Security Series A: Chemistry and Biology, 2012

Essential properties of biosensors for continuous monitoring in blood and tissue are selectivity,... more Essential properties of biosensors for continuous monitoring in blood and tissue are selectivity, sensitivity and biocompatibility. A variety of membranes have been explored to achieve these properties. A good understanding of the diffusion properties of analytes and ...

Journal of Luminescence, 2006

Reactive Al/OH−(aq) interface was studied and used as a source of chemical energy in the generati... more Reactive Al/OH−(aq) interface was studied and used as a source of chemical energy in the generation of chemiluminescence. The observed extrinsic lyoluminescence emission during dissolution of aluminum in an alkaline Tb (III) or Eu (III) chelate solution was clearly based ...

Electroanalysis, 2013

ABSTRACT The properties of electropolymerised phenolic films at amperometric needle electrodes we... more ABSTRACT The properties of electropolymerised phenolic films at amperometric needle electrodes were investigated and their applicability as selective, internal barriers for potential in vivo oxidase enzyme based biosensors evaluated. Polyphenol, poly(phenol red) and dual layer poly(phenol red)/poly(4-aminophenol) films were formed by electropolymerisation and compared with a solvent deposited sulfonated polyether ether sulfonepolyether sulfone (SPEES-PES) membrane. Phenol red had two distinct cyclic voltammetry peaks on platinum: an oxidative peak at +0.70 V and a reduction peak at −0.2 V vs. Ag/AgCl, respectively. Also, the film enhanced the oxidation of hydrogen peroxide by a factor of 3–4, making it an attractive barrier for oxidase based biosensors. Lactate sensors made with polyphenolic electropolymers and solvent deposited SPEES/PES were compared for selectivity and lactate response; the latter showed better selectivity against acetaminophen but less selectivity against ascorbic acid. When sensors were sterilised by standard gamma – irradiation for in vivo application, the polyphenolic films degraded and lost selectivity, whilst SPEES/PES survived unchanged. Salivary lactate was monitored during exercise with electropolymerised film sensors and demonstrated mean lactate increases of 0.3–0.6 mM.

Analytica Chimica Acta, 2002

Cathodic pulse polarisation of oxide-covered aluminium electrodes can generate electrochemilumine... more Cathodic pulse polarisation of oxide-covered aluminium electrodes can generate electrochemiluminescence (ECL) from metalloporphyrins. This is based on the tunnel emission of hot electrons into aqueous electrolyte solution, which probably results in the generation of hydrated electrons as reducing mediators. These tunnel emitted electrons allow the production of highly reactive radicals, such as sulfate radicals from peroxodisulfate ions, which can induce strong redox luminescence from various organic chemiluminophores including metalloporphyrins. The work presented here illustrates the generation of ECL from platinum(II) coproporphyrin (PtCP) and its bovine serum albumin (BSA) conjugate. This allows the detection of these molecules below nanomolar concentrations and over several orders of magnitude of concentration. The relatively long luminescence lifetime of PtCP allows discrimination from the background ECL signal using time resolved measurements, leading to higher sensitivity and the detection of PtCP-BSA indicates the potential use of metalloporphyrins as labels in ECL-based bioassays such as immunoassays and DNA-binding assays.

Analytica Chimica Acta, 2005

Cathodic DC polarization of oxide-covered aluminum produces electrogenerated chemiluminescence fr... more Cathodic DC polarization of oxide-covered aluminum produces electrogenerated chemiluminescence from hydrated and chelated Tb(III) ions in aqueous electrolyte solutions. At the moment of cathodic voltage onset, a strong cathodic flash is observed, which is attributed to a tunnel emission of hot electrons into the aqueous electrolyte solution and the successive chemical reactions with the luminophores. However, within a few milliseconds the insulating oxide film is damaged and finally dissolved due to (i) indiffusion of protons or alkali metal ions into the thin oxide film, (ii) subsequent hydrogen evolution at the aluminum/oxide interface and (iii) alkalization of the electrode surface induced by hydrogen evolution reaction. When the alkalization of the electrode surface has proceeded sufficiently, chemiluminescence is generated with increasing intensity. Aluminum metal, short-lived Al(II), Al(I) or atomic hydrogen and its conjugated base form, hydrated electron, can act as highly reducing species in addition to the less energetic heterogeneously transferred electrons from the aluminum electrode. Tb(III) added as a hydrated ion in the solution probably luminesces in the form of Tb(OH) 3 or Tb(OH) 4 − by direct redox reactions of the central ion whereas multidentate aromatic ligand chelated Tb(III) probably luminesces by ligand sensitized chemiluminescence mechanism in which ligand is first excited by one-electron redox reactions, which is followed by intramolecular energy transfer to the central ion which finally emits light.

Analytica Chimica Acta, 2006

Time-resolved electrogenerated chemiluminescence of multidentate phenolic Eu(III) chelates were s... more Time-resolved electrogenerated chemiluminescence of multidentate phenolic Eu(III) chelates were studied in aqueous solution. 2,6-bis[N,Nbis(carboxymethyl)-aminomethyl]-4-benzoylphenol forms a photoluminescent and electrochemiluminescent Eu(III) chelate, whereas 2,6-bis[N,Nbis(carboxymethyl)-aminomethyl]-4-methyl phenol-chelated Eu(III) turned out to be not luminescent at all. The importance of the redox properties of both the ground and the excited states of the ligands and the central ion is shown. The former chelate shows relatively weak ECL at an oxidecovered aluminum electrode but the ECL intensity can be strongly enhanced by the addition of peroxodisulfate ions. In the presence of 1 mM peroxodisulfate ions the ECL lifetime of this chelate is 0.94 ms, thus easily allowing time-resolved detection of the chelate. This chelate can be conjugated to antibodies by thioureido linkage and used as an electrochemiluminescent label in immunoassays as a marker which displays long-lived luminescence in the red end of the optical spectrum. The present ECL is mainly based on the ligand sensitized redox excitation of the chelate by analogous pathways to those known from the studies of aromatic Tb(III) chelates but the energy transfer from the emission centers of the aluminum oxide film can also have minor contribution to the excitation of the label.

Analytica Chimica Acta, 2002

ABSTRACT Heterogeneous and homogeneous immunoassays of human thyroid stimulating hormone (hTSH) w... more ABSTRACT Heterogeneous and homogeneous immunoassays of human thyroid stimulating hormone (hTSH) were developed on immunometric basis using aromatic Tb(III) chelates as electrochemiluminescent labels and varied types of disposable oxide-covered aluminum electrodes as the solid phase of the immunoassays. The long luminescence lifetime of the present labels allows the use of time-resolved electrochemiluminescence detection and provide the low detection limits of these labels and, thus, sensitive immunoassays. The primary antibody of immunometric immunoassays was coated upon aluminum oxide surface by physical absorption. In homogeneous immunoassays using 66 μl cell and 15 min incubation time, a linear calibration range of 0.25–324 μU/ml was obtained by applying only a single cathodic excitation pulse in the detection step of the assay.

Analytica Chimica Acta, 2002

Hot electrons can be injected from conductor/insulator/electrolyte (C/I/E) junctions into an aque... more Hot electrons can be injected from conductor/insulator/electrolyte (C/I/E) junctions into an aqueous electrolyte solution. Injected hot electrons induce electrogenerated chemiluminescence (ECL) of various luminophores in fully aqueous solutions. Such ECL gives the basis of electrochemiluminoimmunoassays and DNA-probe assays where different luminophores can be used as electrochemiluminescent labels. This work shows that SYBR ® Green I is suitable as an ECL label in detection methods based on C/I/E tunnel-emission electrodes such as oxide-coated aluminium, magnesium and silicon electrodes.

To enable continuous monitoring of electrochemical sensors outside the laboratories, there is a s... more To enable continuous monitoring of
electrochemical sensors outside the laboratories, there is a
significant demand on electrochemical measurement systems to
be miniaturized. The paper presents a low-cost, portable
miniature device for electrochemical measurements. The device
consists of a 35mm x 20mm x 25mm wireless tag, which enables
potentiometric and amperometric measurement, and a base
station for data acquisition. Potentiometric performance is
evaluated using solid contact ion selective electrodes for pH and
sodium. High sensitivity, repeatability and fast response time
have been achieved. Amperometric measurement of hydrogen
peroxide shows that the measured current accuracy and
sensitivity are comparable to that of a commercial potentiostat.
Moreover, the device can be used for lactate concentration
sensing.