Papers by sornambikai sundaram
Electrochimica Acta, 2017
Highly selective, sensitive and low potential detection of biological analytes by simple and rapi... more Highly selective, sensitive and low potential detection of biological analytes by simple and rapid electrochemical technique using low cost nanocarbons is a demanding research since last decade. Herein, we report a low cost, new, nanocarbon, the carbon black (CL-08) functionalized with syringic acid (SA) modified glassy carbon electrode (GCE) for selective L-cysteine (L-CySH) electrocatalysis at 0.04 V vs Ag/AgCl. The new matrix is competitive in the low potential L-CySH detection compared to the multiwalled carbon nanotube, graphite powder, carbon mesoporous and graphitized mesoporous carbon. The possible in situ generated redox products namely 2,6-dimethoxy benzoquinone and 3,4-dihydroxy-5-methoxy benzoic acid were proposed to form on the GCE/SA@CL-08 with two electron transfer and nernstian behaviours. FTIR and UV–vis analyses collectively revealed the presence of quinone species. The GCE/SA@CL-08 showed L-CySH electrocatalysis with good selectivity, 0.42 nA.μM−1 and 5.4 nA.μM−1 sensitivity in the detection range of 20–100 μM and 100–1000 μM respectively with 639 nM limit of detection, in chronoamperometry. A successful demonstration of L-CySH detection from the simulated blood serum and processed chicken samples with substantial recovery values using the GCE/SA@CL-08 were presented in this study.
Nitrite (NO 2 -) is a hazardous chemical often coupled with food sample as a preservative. Azo dy... more Nitrite (NO 2 -) is a hazardous chemical often coupled with food sample as a preservative. Azo dye based colorimetric nitrite detection approaches were quite commonly reported method for colorimetric nitrite analysis. Unfortunately, the above one found to has serious interferences from amine, carboxylic, thiol and carbonyl functional group bearing organic compounds. Here in we found a selective formation of colored product when milli-molar solution of nitrite is reacted with equal concentration of iodide in an acid pH<3. No such coloration was noticed if the iodide is coupled with various biochemicals such as ascorbic acid, citric acid, catechol, cysteine, dopamine, glucose, thiourea, urea and industrial compounds such as nitrite, nitrate, sulfide and chloride. Basic mechanism was probed by using cyclic voltammetry. Iodine was liberated upon the reaction of nitrite with iodide that showed a reddish-yellow colored solution for further nitrite screening. Finally, a simulated fish real sample analysis for screening of nitrite was successfully demonstrated. and easy screening methodology for nitrite based on its selective chemical reaction with iodide in an acidic solution that liberates colored iodine in solution. We extend this work for the detection of nitrite in a fish real sample. This reaction is not interfered by common bio and organic chemicals. To the best of our knowledge such organic selectivity for nitrite screening is not been reported in the literature so for.
Int. J. Electrochem. …, 2011
A copper-gold co-deposited alloy modified screen-printed electrode (SPE/{Cu-Au} nano) coupled flo... more A copper-gold co-deposited alloy modified screen-printed electrode (SPE/{Cu-Au} nano) coupled flow injection analysis (FIA) was developed for sensitive and selective detection of ellagic acid (EA) in cosmetic products. SEM characterization of the working electrode ...
Indian journal of chemistry. Section A, …, 2009
Abstract: Nafion/copper particulates chemically modified glassy carbon electrode has been prepare... more Abstract: Nafion/copper particulates chemically modified glassy carbon electrode has been prepared by in situ electrochemical deposition. The electrode is found to to be successful for selective amperometric sensing of hydrogen peroxide at-0.2 V vs Ag/AgCl at physiological ...
Journal of Nanoscience and Nanotechnology, 2014
Ciprofloxacin (Cf) is a synthetic fourth generation fluoroquinolone class antibiotic used for the... more Ciprofloxacin (Cf) is a synthetic fourth generation fluoroquinolone class antibiotic used for the treatment of gram-positive, gram-negative and mycobacterium species infections. Electrochemical characteristic of the Cf antibiotic on carbon nanotube modified glassy carbon electrode (GCE/CNT) in pH 7 phosphate buffer solution has been investigated. Electrochemically oxidized radical byproduct of the Cf drug, which is formed as intermediate, gets immobilized on the GCE/CNT (GCE/Cf@CNT) and showed stable and well defined surface confined redox peak at − 0.220 V versus Ag/AgCl. Control electrochemical experiment with unmodified GCE failed to show any such immobilization and redox features. Physicochemical characterizations of the Cf@CNT by transmission electron microscope, scanning electron microscope, infrared spectroscopy, UV-Vis and gas chromatography coupled mass spectroscopic analyses of Cf@CNT collectively revealed presence of native form of the Cf antibiotic molecule onto the CNT. The interaction between the Cf molecule and the CNT tubes are revealed from the decreased intensity in the Raman spectrum. The GCE/Cf@CNT showed excellent electrocatalytic response to hydrogen peroxide reduction reaction in pH 7 phosphate buffer solution. Amperometric i-t analysis for the detection of H 2 O 2 showed a current linearity plot upto [H 2 O 2 ] = 200 M at an applied potential − 0.1 V versus Ag/AgCl with a current sensitivity value 678 A mM −1 cm −2 . No interferences were noticed with ascorbic acid, uric acid, cysteine and nitrite. The present study can be highly helpful to understand the interaction between the Cf and H 2 O 2 in physiological systems and for the removal of Cf from the antibiotic polluted water samples especially in the aquaculture and agricultural systems.
Journal of the Electrochemical Society, 2012
Int. J. Electrochem …, 2011
A built-in three-in-one screen-printed electrode assembly containing nano bismuth species deposit... more A built-in three-in-one screen-printed electrode assembly containing nano bismuth species deposited silver as working, pre-oxidized silver as reference and unmodified silver as counter electrodes (designated as SPAgE-Bi nano ), has been developed for simple electrochemical sensing of H 2 O 2 in pH 7 phosphate buffer solution. The working electrode showed ~250 mV reduction in over-potential and a two-fold increased peak current values for electrocatalytic reduction of H 2 O 2 over the respective unmodified silver working electrode (i.e. SPAgE) following a diffusion-controlled electron-transfer mechanism. 50 nm sized Bi particles on SPAgE surface was seen in SEM picture of the working electrode. Linear range of H 2 O 2 detection from 100 µM to 5 mM, a sensitivity of 0.627 µA /mM and detection limit (S/N = 3) of 56.59 µM were obtained. Finally, SPAgE-Bi nano sensor assembly was utilized for cosmetic H 2 O 2 determination, where obtained values and labeled values were in good agreement with recovery in the range of 94.75101.03 %.
The exploration of functional group interactions and electro-generated species stabilization on c... more The exploration of functional group interactions and electro-generated species stabilization on chemically modified electrodes for efficient electro-analytical application is a continuing research area in electrochemistry. In addition, the electrochemical behaviours of the intermediate species, which are generated from the aromatic organic redox mediator and possess both methoxy and amine functional groups, have been rarely studied for electro-analytical applications. For the first time, we report the stabilization of an electro-generated enone derivative of the o-dianisidine (EDo-D) dimer formed as one of the intermediate species during o-dianisidine immobilization. The electro-generated o-dianisidine derivative (o-DD)-stabilized multi-walled carbon nanotube (MWCNT)-modified glassy carbon electrode (GCE/o-DD@MWCNT) exhibited two highly reproducible and, well-defined surface-confined redox couples in a pH 7 phosphate buffer solution (PBS). FTIR analyses indicated the presence of an amine group linkage and an azo product in the o-DD@MWCNT hybrid. UV-Vis and GC-MS analyses confirmed the presence of o-dianisidine in its azo dimer form within the MWCNT. In addition, the enone derivative of the o-dianisidine dimer present on the GCE/o-DD@MWCNT successfully sensed gallic acid (GA) at 0.16 V vs. Ag/AgCl in pH 7 PBS. Highly selective GA detection was achieved with a sensitivity of 0.4580 mA mM À1 , a detection range of 100-1300 mM and a detection limit of 144 nM using chronoamperometry. GCE/o-DD@MWCNT also demonstrated effective GA detection in simulated real grape juice and water samples. Malaysia † Electronic supplementary information (ESI) available: Fig. S1: CV responses of GCE/o-DD@MWCNT from solution phase prepared hybrid powder and its comparison with the in situ prepared electrode, Fig. S2: comparison of the GC-MS spectrum of (A) o-dianisidine and (B) o-DD@MWCNT ltered ethanol extracts, Fig. S3: effect of the scan rate on the GCE/o-DD@MWCNT in the presence of 1 mM GA and Fig. S4: CV response for the effect of the interfering compounds, such as ascorbic acid (AA), uric acid (UA), ellagic acid (EA), dopamine (DA), ferulic acid (FA) and gallic acid (GA) at a concentration of 100 mM, on the GCE/o-DD@MWCNT compared to the GCE/o-DD@MWCNT blank. See Scheme 1 Schematic representation for the formation of possible electro-generated o-dianisidine derivatives (o-DD) on GCE/MWCNT during o-dianisidine immobilization through continuous potential cycling in pH 7 PBS.
A copper-gold co-deposited alloy modified screen-printed electrode (SPE/{Cu-Au} nano ) coupled fl... more A copper-gold co-deposited alloy modified screen-printed electrode (SPE/{Cu-Au} nano ) coupled flow injection analysis (FIA) was developed for sensitive and selective detection of ellagic acid (EA) in cosmetic products. SEM characterization of the working electrode revealed nanostructured dendritic morphology for the alloy on the SPE surface. Cyclic voltammetric response of the SPE/{Cu-Au} nano showed well defined and stable oxidation current signal at 0.1 V vs Ag/AgCl in 0.05 molL -1 NaOH due to complexation of EA with the {Cu-Au} nano alloy particles. Control experiments with Cu or Au modified SPE have failed to show any such marked oxidation response at 0.1 V vs Ag/AgCl. Interrelated FIA parameters including applied potential, flow rate and the electrolyte concentration were systematically optimized for sensitive and selective detection of EA. Under an optimal condition, SPE/{Cu-Au} nano electrode shows a linear calibration plot for EA detection in the window of 0.2-200 mgL -1 with a sensitivity and detection limit value of 0.0657 µA/mgL -1 and 4.1 µgL -1 respectively. A relative standard deviations of 3.95, 3.36 and 3.60% were obtained for ten consecutive injections (n = 10) of 1, 50 and 100 mgL -1 EA, respectively in FIA. Finally, a practical application of the proposed electrode was successfully demonstrated by the quantitative analysis of EA in skin whitening creams with good agreement to that of the labeled values along with appreciable recovery.
A built-in three-in-one screen-printed electrode assembly containing nano bismuth species deposit... more A built-in three-in-one screen-printed electrode assembly containing nano bismuth species deposited silver as working, pre-oxidized silver as reference and unmodified silver as counter electrodes (designated as SPAgE-Bi nano ), has been developed for simple electrochemical sensing of H 2 O 2 in pH 7 phosphate buffer solution. The working electrode showed ~250 mV reduction in over-potential and a two-fold increased peak current values for electrocatalytic reduction of H 2 O 2 over the respective unmodified silver working electrode (i.e. SPAgE) following a diffusion-controlled electron-transfer mechanism. 50 nm sized Bi particles on SPAgE surface was seen in SEM picture of the working electrode. Linear range of H 2 O 2 detection from 100 µM to 5 mM, a sensitivity of 0.627 µA /mM and detection limit (S/N = 3) of 56.59 µM were obtained. Finally, SPAgE-Bi nano sensor assembly was utilized for cosmetic H 2 O 2 determination, where obtained values and labeled values were in good agreement with recovery in the range of 94.75101.03 %.
Nafion/copper particulates chemically modified glassy carbon electrode has been prepared by in si... more Nafion/copper particulates chemically modified glassy carbon electrode has been prepared by in situ electrochemical deposition. The electrode is found to to be successful for selective amperometric sensing of hydrogen peroxide at -0.2 V vs Ag/AgCl at physiological pH without interference from uric acid, ascorbic acid, catechol, cysteine, nitrite and nitrate. Two linear regions, 20-200 µM and 220-400 µM, for H 2 O 2 detection with the slope and regression coefficient values of 33.2 nA/µM and 25.61 nA/µM and 0.9975 and 0.9999 respectively are obtained with 1.63 µM detection limit (S/N = 3). Application to real samples analysis is demonstrated for milk, urine and tea samples with appreciable recovery values.
Ciprofloxacin (Cf) is a synthetic fourth generation fluoroquinolone class antibiotic used for the... more Ciprofloxacin (Cf) is a synthetic fourth generation fluoroquinolone class antibiotic used for the treatment of gram-positive, gram-negative and mycobacterium species infections. Electrochemical characteristic of the Cf antibiotic on carbon nanotube modified glassy carbon electrode (GCE/CNT) in pH 7 phosphate buffer solution has been investigated. Electrochemically oxidized radical byproduct of the Cf drug, which is formed as intermediate, gets immobilized on the GCE/CNT (GCE/Cf@CNT) and showed stable and well defined surface confined redox peak at − 0.220 V versus Ag/AgCl. Control electrochemical experiment with unmodified GCE failed to show any such immobilization and redox features. Physicochemical characterizations of the Cf@CNT by transmission electron microscope, scanning electron microscope, infrared spectroscopy, UV-Vis and gas chromatography coupled mass spectroscopic analyses of Cf@CNT collectively revealed presence of native form of the Cf antibiotic molecule onto the CNT. The interaction between the Cf molecule and the CNT tubes are revealed from the decreased intensity in the Raman spectrum. The GCE/Cf@CNT showed excellent electrocatalytic response to hydrogen peroxide reduction reaction in pH 7 phosphate buffer solution. Amperometric i-t analysis for the detection of H 2 O 2 showed a current linearity plot upto [H 2 O 2 ] = 200 M at an applied potential − 0.1 V versus Ag/AgCl with a current sensitivity value 678 A mM −1 cm −2 . No interferences were noticed with ascorbic acid, uric acid, cysteine and nitrite. The present study can be highly helpful to understand the interaction between the Cf and H 2 O 2 in physiological systems and for the removal of Cf from the antibiotic polluted water samples especially in the aquaculture and agricultural systems.
Electrochemical oxidations of phenol and its derivatives (o-cresol and p-cresol) were examined on... more Electrochemical oxidations of phenol and its derivatives (o-cresol and p-cresol) were examined on a carbon nanotube modified glassy carbon electrode (GCE/CNT) in pH 7 phosphate buffer solution. One of the phenol oxidation byproducts, hydroquinone (HQ) has been immobilized selectively on the GCE/CNT (GCE/HQ@CNT) during the electrochemical oxidation process. The GCE/HQ@CNT showed a stable and well-defined surface confined redox peak at 295 mV vs. Ag/AgCl in pH 7. Amongst the various CNTs viz., impure-multiwalled carbon nanotube (MWCNT), functionalized-MWCNT, purified (p)-MWCNT and single walled CNT examined, the p-MWCNT modified GCE showed best results for the HQ immobilization. Physico-chemical characterizations of the HQ@p-MWCNT by TEM, XPS and FTIR and an in situ electrochemical quartz crystal microbalance studies reveal the presence of unreacted phenol on outer surface and clusters of HQ and {HQ-biphenol} species inside the walls of the HQ@p-MWCNT hybrid material. The GCE/HQ@p-MWCNT showed highly selective electrocatalytic oxidation of hydrazine through the mediation of the immobilized HQ/quinone redox species, without any interference from cysteine, ascorbic acid, uric acid, dopamine, nitrite, nitrate and hydrogen peroxide. Control experiments with GCE/MWCNT and GCE have failed to show any such electrocatalysis to hydrazine. Most interestingly, twice higher antibacterial activity towards the Escherichia coli bacteria over the native phenol was noticed on the HQ@CNT. These results indicate potential applicability of the HQ@CNT as hydrazine sensor and thin-film based antibacterial agent. oxidation pathways were also reported in the literatures. For the electrochemical oxidation purpose, metallic electrodes like platinum [26], gold [26,27], Ni-Nb-Pt-Sn alloy [28], boron doped diamond [29], glassy carbon (GCE) [30] and stainless steel [31]
An electrochemical route for highly selective immobilization of a b-lactam family antibiotic,
amo... more An electrochemical route for highly selective immobilization of a b-lactam family antibiotic,
amoxicillin (AMX), from the other drugs, penicillin and ampicillin, on multiwalled carbon nanotube
modified glassy carbon electrodes (GCE/AMX@MWNT), without any linkers and surface
functionalization, has been successfully demonstrated. The electrochemical response of the AMX on
GCE/MWNT showed an irreversible oxidation peak at 0.5 V vs. Ag/AgCl (A1), followed by the growth
of a new redox peak at 0 V vs. Ag/AgCl (A2/C2) in pH 7 phosphate buffer solution, which is in parallel
to a control phenol electrochemical response, revealed that the phenoxy radical electrogenerated at A1
gets subsequently adsorbed on the underlying MWNT modified electrode with a specific surface
confined A2/C2 redox peak with proton-coupled electron transfer behaviour. Physicochemical
characterization from X-ray diffraction, transmission electron microscopy and scanning electron
microscopy collectively evidenced the immobilization of AMX both on the inner and outer (surface)
walls of the carbon nanotubes. Further, the AMX@MWNT hybrid material was found to show
enhanced antibacterial activity against three bacterial pathogens, Escherichia coli, Staphylococcus
aureus and Bacillus subtilis, over the unmodified AMX and MWNT. Finally, as an environmental
pollution remedy, the uptake of the AMX drug from five different simulated sources: river water, sea
water, river soil, sea soil and farm milk, was successfully demonstrated by this new electrochemical
methodology.
Electrochemical immobilization of 4-nitrophenol (4-NP) was
conducted on a purified multi-walled ca... more Electrochemical immobilization of 4-nitrophenol (4-NP) was
conducted on a purified multi-walled carbon nanotube
(p-MWCNT) modified glassy carbon electrode (GCE/p-MWCNT) in
pH 7 phosphate buffer solution (PBS). The electrochemical
reduction of 4-NP to stable in situ electrogenerated hydroxylamine
(ØNHOH) intermediate species within the p-MWCNT matrix
may be the underlying mechanism of immobilization. The
ØNHOH-stabilized p-MWCNT modified electrode, GCE/
ØNHOH@p-MWCNT, showed stable and well-defined surfaceconfined
redox peaks at 0.11 V (A1/C1) and 0.080 V (A2/C2) vs.
Ag/AgCl over other CNT-modified GCEs. The modified electrode
system suggested quasi-reversible and reversible electron transfer
mechanisms for the A1/C1 and A2/C2 redox couples. TEM
analysis of the ØNHOH@p-MWCNT hybrid powder demonstrated
the presence of ØNHOH species on the surfaces, as well as on the
inner walls of the p-MWCNTs. The XRD peaks exhibited shifts in 2q
values for the hybrid material compared with the unmodified
materials, which confirmed the stabilization of ØNHOH within the
p-MWCNT via p–p interactions. Electrochemical characterization
of the GCE/ØNHOH@p-MWCNT revealed two electron transfer
mechanisms with adsorption-controlled and Nernstian behav-
iours. A highly sensitive electrocatalytic oxidation of dihydronicotinamide
adenine dinucleotide (NADH) at 0.02 V vs. Ag/
AgCl was achieved with the GCE/ØNHOH@p-MWCNT. Furthermore,
the hybrid electrode successfully sensed NADH amperometrically
with 2.9 nA mM
1
sensitivity, a 0.043 mM limit of detection and a linear detection range from 100 mMto1mMfor
ten successive additions of 100 mM NADH at an applied potentialof 0.02 V vs. Ag/AgCl in pH 7 PBS.
Journal of Electroanalytical Chemistry, 2010
Here in, we are reporting simple, selective and direct immobilization of a biological redox media... more Here in, we are reporting simple, selective and direct immobilization of a biological redox mediator, catechol (1,2-dihydroxy phenol, CA), on glassy carbon electrode (GCE) and screen-printed carbon electrode (SPCE) surfaces through electrochemical oxidation procedures in aqueous solutions without any other external matrix. The CA immobilized activated carbon electrodes (GCE*–CAads and SPCE*–CAads) have shown well-defined and stable surface confined redox behavior centered (Eo′) at ∼0.05 V vs Ag/AgCl and peak-to-peak separation (ΔEp) of ∼20 mV in pH 7 PBS. This observation is selective for CA on the carbon surfaces. Control experiments with other hydroxyl phenols including, Dopamine and Resorcinol failed to show any such adsorption or immobilization on the carbon surfaces. XPS and ATIR/FTIR characterization implies covalent immobilization of the C-4 of the CA through carboxylic functional group of the activated surfaces.
Electroanalysis, 2010
A screen-printed silver strip with a built-in three-in-one electrode (SPAgE) configuration of Ag-... more A screen-printed silver strip with a built-in three-in-one electrode (SPAgE) configuration of Ag-working, Ag-counter and Ag/AgxO (silver oxides) pseudoreference electrodes has been developed for sensitive and selective electrochemical flow injection analysis (FIA) of aluminum chlorohydrate (ACH) present in antiperspirants, through the free Cl− ion liberated from ACH in aqueous medium, as a redox signal at Ag-working electrode in pH 6 phosphate buffer solution (PBS). The solution phase and instrumental parameters were systematically optimized. The calibration graph was linear in the window 1–200 ppm concentration of ACH and the lowest detection limit (S/N=3) was 295 ppb with a slope of 0.0989 μA/ppm and regression coefficient of 0.998. Calculated relative standard deviation (RSD) values for the detection of 5 and 50 ppm ACH by this method are 2.21 % and 2.16 %, respectively. Four different antiperspirant deodorants real samples with and without ACH content were successfully analyzed and the detected values obtained were found to be in good agreement with the product labeled values.
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Papers by sornambikai sundaram
amoxicillin (AMX), from the other drugs, penicillin and ampicillin, on multiwalled carbon nanotube
modified glassy carbon electrodes (GCE/AMX@MWNT), without any linkers and surface
functionalization, has been successfully demonstrated. The electrochemical response of the AMX on
GCE/MWNT showed an irreversible oxidation peak at 0.5 V vs. Ag/AgCl (A1), followed by the growth
of a new redox peak at 0 V vs. Ag/AgCl (A2/C2) in pH 7 phosphate buffer solution, which is in parallel
to a control phenol electrochemical response, revealed that the phenoxy radical electrogenerated at A1
gets subsequently adsorbed on the underlying MWNT modified electrode with a specific surface
confined A2/C2 redox peak with proton-coupled electron transfer behaviour. Physicochemical
characterization from X-ray diffraction, transmission electron microscopy and scanning electron
microscopy collectively evidenced the immobilization of AMX both on the inner and outer (surface)
walls of the carbon nanotubes. Further, the AMX@MWNT hybrid material was found to show
enhanced antibacterial activity against three bacterial pathogens, Escherichia coli, Staphylococcus
aureus and Bacillus subtilis, over the unmodified AMX and MWNT. Finally, as an environmental
pollution remedy, the uptake of the AMX drug from five different simulated sources: river water, sea
water, river soil, sea soil and farm milk, was successfully demonstrated by this new electrochemical
methodology.
conducted on a purified multi-walled carbon nanotube
(p-MWCNT) modified glassy carbon electrode (GCE/p-MWCNT) in
pH 7 phosphate buffer solution (PBS). The electrochemical
reduction of 4-NP to stable in situ electrogenerated hydroxylamine
(ØNHOH) intermediate species within the p-MWCNT matrix
may be the underlying mechanism of immobilization. The
ØNHOH-stabilized p-MWCNT modified electrode, GCE/
ØNHOH@p-MWCNT, showed stable and well-defined surfaceconfined
redox peaks at 0.11 V (A1/C1) and 0.080 V (A2/C2) vs.
Ag/AgCl over other CNT-modified GCEs. The modified electrode
system suggested quasi-reversible and reversible electron transfer
mechanisms for the A1/C1 and A2/C2 redox couples. TEM
analysis of the ØNHOH@p-MWCNT hybrid powder demonstrated
the presence of ØNHOH species on the surfaces, as well as on the
inner walls of the p-MWCNTs. The XRD peaks exhibited shifts in 2q
values for the hybrid material compared with the unmodified
materials, which confirmed the stabilization of ØNHOH within the
p-MWCNT via p–p interactions. Electrochemical characterization
of the GCE/ØNHOH@p-MWCNT revealed two electron transfer
mechanisms with adsorption-controlled and Nernstian behav-
iours. A highly sensitive electrocatalytic oxidation of dihydronicotinamide
adenine dinucleotide (NADH) at 0.02 V vs. Ag/
AgCl was achieved with the GCE/ØNHOH@p-MWCNT. Furthermore,
the hybrid electrode successfully sensed NADH amperometrically
with 2.9 nA mM
1
sensitivity, a 0.043 mM limit of detection and a linear detection range from 100 mMto1mMfor
ten successive additions of 100 mM NADH at an applied potentialof 0.02 V vs. Ag/AgCl in pH 7 PBS.
amoxicillin (AMX), from the other drugs, penicillin and ampicillin, on multiwalled carbon nanotube
modified glassy carbon electrodes (GCE/AMX@MWNT), without any linkers and surface
functionalization, has been successfully demonstrated. The electrochemical response of the AMX on
GCE/MWNT showed an irreversible oxidation peak at 0.5 V vs. Ag/AgCl (A1), followed by the growth
of a new redox peak at 0 V vs. Ag/AgCl (A2/C2) in pH 7 phosphate buffer solution, which is in parallel
to a control phenol electrochemical response, revealed that the phenoxy radical electrogenerated at A1
gets subsequently adsorbed on the underlying MWNT modified electrode with a specific surface
confined A2/C2 redox peak with proton-coupled electron transfer behaviour. Physicochemical
characterization from X-ray diffraction, transmission electron microscopy and scanning electron
microscopy collectively evidenced the immobilization of AMX both on the inner and outer (surface)
walls of the carbon nanotubes. Further, the AMX@MWNT hybrid material was found to show
enhanced antibacterial activity against three bacterial pathogens, Escherichia coli, Staphylococcus
aureus and Bacillus subtilis, over the unmodified AMX and MWNT. Finally, as an environmental
pollution remedy, the uptake of the AMX drug from five different simulated sources: river water, sea
water, river soil, sea soil and farm milk, was successfully demonstrated by this new electrochemical
methodology.
conducted on a purified multi-walled carbon nanotube
(p-MWCNT) modified glassy carbon electrode (GCE/p-MWCNT) in
pH 7 phosphate buffer solution (PBS). The electrochemical
reduction of 4-NP to stable in situ electrogenerated hydroxylamine
(ØNHOH) intermediate species within the p-MWCNT matrix
may be the underlying mechanism of immobilization. The
ØNHOH-stabilized p-MWCNT modified electrode, GCE/
ØNHOH@p-MWCNT, showed stable and well-defined surfaceconfined
redox peaks at 0.11 V (A1/C1) and 0.080 V (A2/C2) vs.
Ag/AgCl over other CNT-modified GCEs. The modified electrode
system suggested quasi-reversible and reversible electron transfer
mechanisms for the A1/C1 and A2/C2 redox couples. TEM
analysis of the ØNHOH@p-MWCNT hybrid powder demonstrated
the presence of ØNHOH species on the surfaces, as well as on the
inner walls of the p-MWCNTs. The XRD peaks exhibited shifts in 2q
values for the hybrid material compared with the unmodified
materials, which confirmed the stabilization of ØNHOH within the
p-MWCNT via p–p interactions. Electrochemical characterization
of the GCE/ØNHOH@p-MWCNT revealed two electron transfer
mechanisms with adsorption-controlled and Nernstian behav-
iours. A highly sensitive electrocatalytic oxidation of dihydronicotinamide
adenine dinucleotide (NADH) at 0.02 V vs. Ag/
AgCl was achieved with the GCE/ØNHOH@p-MWCNT. Furthermore,
the hybrid electrode successfully sensed NADH amperometrically
with 2.9 nA mM
1
sensitivity, a 0.043 mM limit of detection and a linear detection range from 100 mMto1mMfor
ten successive additions of 100 mM NADH at an applied potentialof 0.02 V vs. Ag/AgCl in pH 7 PBS.