Characterization of glassy carbon electrodes modified with carbon nanotubes and iron phthalocyanine through grafting and click chemistry

Carbon Electrode-Based Biosensing Enabled by Biocompatible Surface Modification with DNA and Proteins

Modification of electrodes with biomolecules is an essential first step for the development of bioelectrochemical systems, which are used in a variety of applications ranging from sensors to fuel cells. Gold is often used because of its ease of modification with thiolated biomolecules, but carbon screen-printed electrodes (SPEs) are gaining popularity due to their low cost and fabrication from abundant resources. However, their effective modification with biomolecules remains a challenge; the majority of work to-date relies on nonspecific adhesion or broad amide bond formation to chemical handles on the electrode surface. By combining facile electrochemical modification to add an aniline handle to electrodes with a specific and biocompatible oxidative coupling reaction, we can readily modify carbon electrodes with a variety of biomolecules. Importantly, both proteins and DNA maintain bioactive conformations following coupling. We have then used biomolecule-modified electrodes to generate microbial monolayers through DNA-directed immobilization. This work provides an easy, general strategy to modify inexpensive carbon electrodes, significantly expanding their potential as bioelectrochemical systems.

A Synergistic Effect of Phthalimide-Substituted Sulfanyl Porphyrazines and Carbon Nanotubes to Improve the Electrocatalytic Detection of Hydrogen Peroxide

A sulfanyl porphyrazine derivative with peripheral phthalimide moieties was metallated with cobalt(II) and iron(II) metal ions. The purity of the macrocycles was confirmed by HPLC, and subsequently, compounds were characterized using various analytical methods (ES-TOF, MALDI-TOF, UV–VIS, and NMR spectroscopy). To obtain hybrid electroactive electrode materials, novel porphyrazines were combined with multiwalled carbon nanotubes. The electrocatalytic effect derived from cobalt(II) and iron(II) cations was evaluated. As a result, a significant decrease in the overpotential was observed compared with that obtained with bare glassy carbon (GC) or glassy carbon electrode/carbon nanotubes (GC/MWCNTs), which allowed for sensitive determination of hydrogen peroxide in neutral conditions (pH 7.4). The prepared sensor enables a linear response to H₂O₂ concentrations of 1–90 µM. A low detection limit of 0.18 μM and a high sensitivity of 640 μA mM⁻¹ cm⁻² were obtained. These results indicate that the obtained sensors could potentially be applied in biomedical and environmental fields.

Charge-Transfer Spectroscopy of Bisaxially Coordinated Iron(II) Phthalocyanines through the Prism of the Lever's EL Parameters Scale, MCD Spectroscopy, and TDDFT Calculations

The position of the experimentally observed (in the UV-vis and magnetic circular dichroism (MCD) spectra) low-energy metal-to-ligand charge-transfer (MLCT) band in low-spin iron(II) phthalocyanine complexes of general formula PcFeL₂, PcFeL'L″, and [PcFeX₂]^2- (L, L', or L″ are neutral and X^- is an anionic axial ligand) was correlated with the Lever's electrochemical E_L scale values for the axial ligands. The time-dependent density functional theory (TDDFT)-predicted UV-vis spectra are in very good agreement with the experimental data for all complexes. In the majority of compounds, TDDFT predicts that the first degenerate MLCT band that correlates with the MCD A-term observed between 360 and 480 nm is dominated by an e_g (Fe, d_π) → b_1u (Pc, π*) single-electron excitation (in traditional D_4h point group notation) and agrees well with the previous assignment discussed by Stillman and co-workers[ Inorg. Chem. 1994, 33, 573-583]. The TDDFT calculations also suggest a small energy gap for b_1u/b_2u (Pc, π*) orbital splitting and closeness of the MLCT₁ e_g (Fe, d_π) → b_1u (Pc, π*) and MLCT₂ e_g (Fe, d_π) → b_2u (Pc, π*) transitions. In the case of the PcFeL₂ complexes with phosphines as the axial ligands, additional degenerate charge-transfer transitions were observed between 450 and 500 nm. These transitions are dominated by a_2u (Pc + L, π) → e_g (Pc, π*) single-electron excitations and are unique for the PcFe(PR₃)₂ complexes. The energy of the phthalocyanine-based a_2u orbital has large axial ligand dependency and is the reason for a large energy deviation for B1 a_2u (Pc + L, π) → e_g (Pc, π*) transition. The energies of the axial ligand-to-iron, axial ligand-to-phthalocyanine, iron-to-axial ligand, and phthalocyanine-to-axial ligand charge-transfer transitions were discussed on the basis of TDDFT calculations.

The synergistic effects of coupling Au nanoparticles with an alkynyl Co(II) phthalocyanine on the detection of prostate specific antigen

Prostate specific antigen (PSA) aptasensors are fabricated using a novel asymmetrically substituted Co phthalocyanine (CoPc), gold nanoparticles (AuNPs) and PSA-specific antigen. The fabricated aptasensors are: GCE-AuNPs-Aptamer, GCE@CoPc-Aptamer and GCE-AuNPs@CoPc-Aptamer (GCE = glassy carbon electrode). The fabricated sensors are characterized at each modification step to monitor the changes occurring at the sensor surface. Concentration studies were carried out using differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) to determine detection limits. All the fabricated aptasensors were found to be highly specific and selective but the GCE-AuNPs@CoPc-Aptamer nanoconjugate performed the best. The aptasensors were also tested in spiked serum samples and detection limits, as well as % recoveries were determined. The results obtained showed that the GCE-AuNPs@CoPc-Aptamer has the potential to be used for clinical studies as the results agree with those obtained for detection of PSA in buffer.

Role of Iron Phthalocyanine Coordination in Catecholamines Detection

Catecholamines are an important class of neurotransmitters responsible for regularizing, controlling, and treating neural diseases. Based on control and diseases treatment, the development of methodology and dives to sensing is a promissory technology area. This work evaluated the role of iron phthalocyanine coordination (FePc) with the specific groups from catecholamine molecules (L-dopa, dopamine, epinephrine, and the amino acid tyrosine) and the effect of this coordination on electrochemical behavior. The in situ coordination analysis was performed through isotherms π-A of FePc Langmuir films in the absence and presence of catecholamines. The π-A isotherm indicates a strong interaction between FePc monolayer and L-Dopa and DA, which present a catechol group and a side chain with a protonated amino group (-NH3+). These strong interactions with catechol and amine groups were confirmed by characterization at the molecular level using the surface-enhanced Raman spectroscopy (SERS) from a Langmuir–Schaefer monolayer deposited onto Ag surfaces. The electrochemical measurements present a similar tendency, with lower oxidation potential observed to DA>L-Dopa>Ep. The results corroborate that the coordination of the analyte on the electron mediator surface plays an essential role in an electrochemical sensing application. The FePc LS film was applied as a sensor in tablet drug samples, showing a uniformity of content of 96% for detecting active compounds present in the L-Dopa drug samples.

Application of Lever's EL Parameter Scale toward Fe(II)/Fe(III) versus Pc(2-)/Pc(1-) Oxidation Process Crossover Point in Axially Coordinated Iron(II) Phthalocyanine Complexes

The electronic structures and, particularly, the nature of the HOMO in a series of PcFeL₂, PcFeL'L″, and [PcFeX₂]^2- complexes (Pc = phthalocyaninato(2-) ligand; L = NH₃, n-BuNH₂, imidazole (Im), pyridine (Py), PMe₃, PBu₃, t-BuNC, P(OBu)₃, and DMSO; L' = CO; L″ = NH₃ or n-BuNH₂; X = NCO^-, NCS^-, CN^-, imidazolate (Im^-), or 1,2,4-triazolate(Tz^-)) were probed by electrochemical, spectroelectrochemical, and chemical oxidation as well as theoretical (density functional theory, DFT) studies. In general, energies of the metal-centered occupied orbitals in various six-coordinate iron phthalocyanine complexes correlate well with Lever Electrochemical Parameter E_L and intercross the phthalocyanine-centered a_1u orbital in several compounds with moderate-to-strong π-accepting axial ligands. In these cases, an oxidation of the phthalocyanine macrocycle (Pc(2-)/Pc(1-)) rather than the central metal ion (Fe(II)/Fe(III)) was theoretically predicted and experimentally confirmed.

Building Tailored Interfaces through Covalent Coupling Reactions at Layers Grafted from Aryldiazonium Salts

Aryldiazonium ions are widely used reagents for surface modification. Attractive aspects of their use include wide substrate compatibility (ranging from plastics to carbons to metals and metal oxides), formation of stable covalent bonding to the substrate, simplicity of modification methods that are compatible with organic and aqueous solvents, and the commercial availability of many aniline precursors with a straightforward conversion to the active reagent. Importantly, the strong bonding of the modifying layer to the surface makes the method ideally suited to further on-surface (postfunctionalization) chemistry. After an initial grafting from a suitable aryldiazonium ion to give an anchor layer, a target species can be coupled to the layer, hugely expanding the range of species that can be immobilized. This strategy has been widely employed to prepare materials for numerous applications including chemical sensors, biosensors, catalysis, optoelectronics, composite materials, and energy conversion and storage. In this Review our goal is first to summarize how a target species with a particular functional group may be covalently coupled to an appropriate anchor layer. We then review applications of the resulting materials.

Accurate Prediction of Mössbauer Hyperfine Parameters in Bis-Axially Coordinated Iron(II) Phthalocyanines Using Density Functional Theory Calculations: A Story of a Single Orbital Revealed by Natural Bond Orbital Analysis

Density Functional Theory (DFT) calculations coupled with several exchange-correlation functionals were used for the prediction of Mössbauer hyperfine parameters of 36 bis-axially coordinated iron(II) phthalocyanine complexes with the general formulas PcFeL₂, PcFeL'L″, and [PcFeX₂]^2-, including four new compounds. Both gas-phase and PCM calculations using BPW91 and MN12L exchange-correlation functionals were found to accurately predict both Mössbauer quadrupole splittings and the correct trends in experimentally observed isomer shifts. In comparison, hybrid exchange-correlation functionals underestimated quadrupole splittings, while still accurately predicted isomer shifts. Out of ∼40 exchange-correlation functionals tested, only MN12L was found to correctly reproduce quadrupole splitting trends in the PcFeL₂ complexes coordinated with phosphorus-donor axial ligands (i.e., P(OnBu)₃ ≈ P(OEt)₃ < PMe₃ < P[(CH₂O)₂CH₂]-p-C₆H₄NO₂ < PEt₃ ≈ PnBu₃). Natural Bond Orbital (NBO) analysis was successfully used to explain the general trends in the observed quadrupole splitting for all compounds of interest. In particular, the general trends in the quadrupole splitting correlate well with the axial ligand dependent, NBO-predicted population of the 3d_z2 orbital of the Fe ion and are reflective of the hypothesis proposed by Ohya and co-workers ( Inorg. Chem., 1984, 23, 1303) on the adaptability of the phthalocyanine's π-system toward Fe-L_ax interactions. The first X-ray crystal structure of a PcFeL₂ complex with axial phosphine ligands is also reported.

A career in photophysicochemical and electrochemical properties of phthalocyanine — a Linstead Career Award paper

This manuscript highlights the author’s contributions to phthalocyanine chemistry, especially the applications based on their electrochemistry and photophysicochemistry. In particular, the use of phthalocyanines as electrocatalysts and photocatalysts is presented. For photocatalysis, photodynamic antimicrobial chemotherapy and pollution control using green technologies are highlighted. For electrocatalysis the phthalocyanines are employed for the detection of pollutants and environmentally important molecules. Phthalocyanines are combined with nanomaterials for improved photocatalysis and electrocatalysis.

Enhanced electrocatalytic activity of cobalt phthalocyanines when “clicked” to graphene oxide nanosheets

Alkyne-terminated Co phthalocyanine (CoPc) derivatives are linked to reduced graphene oxide nanosheets (GONS) via click chemistry and the conjugates are used for the electrocatalytic oxidation of 2-mercaptoethanol. CoPc derivatives where the alkyne group is separated from the Pc ring by an aliphatic and benzene ring (complex 3) showed the best catalytic activity (in terms of oxidation potential) in comparison to when only aliphatic chains were employed without the benzene ring (complex 2) and when there were no substituents (complex 1). The anodic oxidation of 2-mercaptoethanol on 3-GONS (linked) occurred at the least positive oxidation potential (-0.22 V vs. Ag|AgCl). 3-GONS (linked) was found to have the highest sensitivity with the lowest limit of detection of 0.08 [Formula: see text]M. When the CoPc derivative and GONS were not linked but placed sequentially on the electrode, the electrocatalytic activity (in terms of LOD) was poorer than when linked. The electrodes modified with CoPc clicked to GONS are highly promising electrochemical sensors in terms of stability, sensitivity, good catalytic activity and ease of fabrication.

Copper(I)-Catalyzed Click Chemistry as a Tool for the Functionalization of Nanomaterials and the Preparation of Electrochemical (Bio)Sensors

Proper functionalization of electrode surfaces and/or nanomaterials plays a crucial role in the preparation of electrochemical (bio)sensors and their resulting performance. In this context, copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) has been demonstrated to be a powerful strategy due to the high yields achieved, absence of by-products and moderate conditions required both in aqueous medium and under physiological conditions. This particular chemistry offers great potential to functionalize a wide variety of electrode surfaces, nanomaterials, metallophthalocyanines (MPcs) and polymers, thus providing electrochemical platforms with improved electrocatalytic ability and allowing the stable, reproducible and functional integration of a wide range of nanomaterials and/or different biomolecules (enzymes, antibodies, nucleic acids and peptides). Considering the rapid progress in the field, and the potential of this technology, this review paper outlines the unique features imparted by this particular reaction in the development of electrochemical sensors through the discussion of representative examples of the methods mainly reported over the last five years. Special attention has been paid to electrochemical (bio)sensors prepared using nanomaterials and applied to the determination of relevant analytes at different molecular levels. Current challenges and future directions in this field are also briefly pointed out.

Functionalization of nanomaterials with aryldiazonium salts

This paper reviews the surface modification strategies of a wide range of nanomaterials using aryldiazonium salts. After a brief history of diazonium salts since their discovery by Peter Griess in 1858, we will tackle the surface chemistry using these compounds since the first trials in the 1950s. We will then focus on the modern surface chemistry of aryldiazonium salts for the modification of materials, particularly metallic, semiconductors, metal oxide nanoparticles, carbon-based nanostructures, diamond and clays. The successful modification of sp(2) carbon materials and metals by aryldiazonium salts paved the way to innovative strategies for the attachment of aryl layers to metal oxide nanoparticles and nanodiamonds, and intercalation of clays. Interestingly, diazotized surfaces can easily trap nanoparticles and nanotubes while diazotized nanoparticles can be (electro)chemically reduced on electrode/materials surfaces as molecular compounds. Both strategies provided organized 2D surface assembled nanoparticles. In this review, aryldiazonium salts are highlighted as efficient coupling agents for many types of molecular, macromolecular and nanoparticulate species, therefore ensuring stability to colloids on the one hand, and the construction of composite materials and hybrid systems with robust and durable interfaces/interphases, on the other hand. The last section is dedicated to a selection of patents and industrial products based on aryldiazonium-modified nanomaterials. After nearly 160 years of organic chemistry, diazonium salts have entered a new, long and thriving era for the benefit of materials, colloids, and surface scientists. This tempts us to introduce the terminology of "diazonics" we define as the science and technology of aryldiazonium salt-derived materials.

Evaluation of amperometric dot microsensors for the analysis of folic acid in pharmaceutical tablets and urine samples

Nineteen amperometric dot microsensors based on graphite and graphene modified with a selection of porphyrins and phthalocyanines were evaluated and tested for their ability of the analysis of folic acid in pharmaceutical tablets (e.g. Acifol) and biological samples (e.g. urine), using differential pulse voltammetry. Cyclic voltammetry was used to optimize the working conditions, e.g. pH and electrolyte for the proposed amperometric dot microsensors. The optimum working pH was 7.0 (phosphate buffer), with a 0.1 M potassium chloride supporting electrolyte. The linear concentration ranges for folic acid were between 10-6 and 10-3) M for all dot microsensors except dot microsensors based on graphite modified with tetraamino cobalt(II) phthalocyanine and tetranitro manganese(II) phthalocyanine which had linear concentration ranges between 10-6 and 10-4 M . The highest sensitivity (0.770 nA. mmolL-1) was recorded for the graphite modified with tetraamino cobalt(II) phthalocyanine based dot sensor and the lowest limit of detection (1.14 10-7 M ) for the graphite modified with tetranitro zinc(II) phthalocyanine based dot sensor. The dot sensors were used for the reliable analysis of folic acid in Acifol tablets and urine samples, with recoveries higher than 94.00% and 99.00%, respectively.

p-Aminophenol sensor based on tetra-β-[3-(dimethylamine)phenoxy] phthalocyanine cobalt(ii)/multiwalled carbon nanotube hybrid

The hybrid tetra-β-[3-(dimethylamine)phenoxy] phthalocyanine cobalt(ii)/multiwalled carbon nanotube was designed and synthesized, which can serve as an efficient catalyst for sensitive p-aminophenol detection due to synergistic effects between phthalocyanine and the carbon.

Zinc phthalocyanines with fluorinated substituents for direct sensing of carbamate and organophosphate pesticides in water

Water pollution by pesticides as the result of intensive agriculture and horticulture has brought many negative consequences to humans and ecosystems. Among others, chemical sensor systems are under intense development for direct pesticide analysis in aqueous samples as a cost effective and simple alternative analytical method. In this work, a set of zinc phthalocyanines is studied in its liquid sensing properties using quartz crystal microbalances. Four different species selected from the two most common organophosphorus and carbamate classes of pesticides are used as test analytes. The phthalocyanines are chemically modified with different fluorinated substituents to increase sensor sensitivity and govern pesticide selectivity in order to create sensors with widely diverging analyte responses. By this means, sensors with a general high sensitivity and selectivity for the two pesticide classes were obtained and detection limits down to 0.03 mg.L-1 could be achieved. The response data of the sensors are analyzed in detail using exploratory multivariate data evaluation methods. The results show that phthalocyanine based sensors are a truly capable platform for chemical analysis systems of aqueous samples.