A breakthrough electrochemical sensor combining nanotechnology and molecular engineering for precise isoniazid detection
Tuberculosis remains a persistent global health challenge, with isoniazid (INH) as one of the first-line defense medications against this infectious disease.
Proper dosage monitoring is critical—too little medication leads to treatment failure and drug resistance, while too much can cause liver damage and other side effects. Unfortunately, conventional methods for detecting isoniazid in biological samples like blood plasma often involve complicated procedures requiring sophisticated laboratory equipment, trained personnel, and time-consuming processes.
At the heart of this innovative sensor are multi-walled carbon nanotubes (MWCNTs)—remarkable cylindrical nanostructures composed of rolled graphene sheets. These nanotubes possess extraordinary electrical conductivity, making them ideal for electrochemical applications where efficient electron transfer is crucial.
Their unique structure provides an exceptionally high surface area, allowing more opportunities for molecules to interact with the sensor surface. Additionally, the ability to functionalize these nanotubes—chemically modifying their surfaces with specific functional groups like oxygen or amine groups—makes them even more versatile for sensor design 4 .
Iron phthalocyanine (FePc) belongs to a class of complex molecules known as metallophthalocyanines, which share a structural resemblance to the heme group in hemoglobin. These molecules exhibit outstanding electrocatalytic properties, meaning they can significantly enhance specific chemical reactions when a voltage is applied.
The iron atom at the center of the phthalocyanine ring acts as an active catalytic site, facilitating the oxidation of target molecules like isoniazid. While FePc alone suffers from poor electrical conductivity and tends to form aggregates, when properly supported on appropriate materials, it becomes an exceptionally powerful catalyst 2 4 .
| Property | Carbon Nanotubes | Iron Phthalocyanine | Composite Advantage |
|---|---|---|---|
| Electrical Conductivity | Excellent | Poor | MWCNTs provide electron transfer pathway |
| Catalytic Activity | Limited | Excellent | FePc provides specific catalytic sites |
| Surface Area | Very High | Low (tends to aggregate) | MWCNTs prevent FePc aggregation |
| Stability | High | High | Combined structure enhances durability |
When researchers combine functionalized MWCNTs with iron phthalocyanine, they create a composite material with properties greater than the sum of its parts. The carbon nanotubes provide the structural backbone and electron transfer highway, while the iron phthalocyanine molecules offer specific catalytic activity toward isoniazid.
This partnership creates a synergistic effect where the components complement each other's strengths and mitigate their individual limitations.
Studies have shown that the association of carbon nanotubes with other catalytic materials like tungsten disulfide (WS₂) can produce composites with excellent conductivity and large surface area, significantly enhancing electrocatalytic responses to target molecules 1 . Similarly, the combination with iron phthalocyanine creates a nanocomposite that demonstrates remarkable sensitivity toward isoniazid detection.
The interaction between these components typically occurs through π-π stacking—a molecular-level phenomenon where the planar phthalocyanine rings align with the hexagonal carbon structures of the nanotubes through electron cloud interactions. In some cases, researchers have also explored forming axial covalent bonds between the carbon matrix and the metal-N₄ macrocycles to further stabilize the iron atoms and prevent aggregation 2 .
MWCNTs provide efficient pathways for electron transport during electrochemical reactions.
π-π stacking enables strong interaction between FePc molecules and carbon nanotube surfaces.
The composite shows significantly improved sensitivity compared to individual components.
The MWCNTs first undergo chemical treatment to introduce oxygen-containing functional groups on their surfaces. This is typically achieved through oxidation using strong acids like nitric acid or through the Hummer method, which makes the nanotube surfaces more reactive and better able to interact with the iron phthalocyanine molecules 2 4 .
The functionalized nanotubes are then combined with an iron phthalocyanine solution. This can be done through a simple liquid chemical reaction at room temperature or sometimes with additional hydrothermal treatment to enhance the integration. The FePc molecules uniformly disperse on the nanotube surfaces, creating the active nanocomposite 2 .
The nanocomposite is then deposited onto an electrode surface—typically a glassy carbon electrode or screen-printed carbon electrode. This is often done using a technique called drop-casting, where a precise volume of the composite suspension is applied to the electrode and allowed to dry, forming a uniform film 3 5 .
The modified electrode undergoes rigorous testing using techniques like Raman spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy to confirm the successful integration of materials and to analyze the surface properties 1 .
| Step | Process | Purpose | Common Methods |
|---|---|---|---|
| 1 | CNT Functionalization | Introduce reactive sites on nanotubes | Acid treatment, Hummer method |
| 2 | FePc Anchoring | Create active nanocomposite | Liquid chemical reaction, Hydrothermal treatment |
| 3 | Electrode Modification | Apply composite to sensor platform | Drop-casting, Spin coating |
| 4 | Characterization | Verify successful fabrication | Raman spectroscopy, SEM, XPS |
Raman Spectroscopy
SEM Analysis
The research team employed cyclic voltammetry (CV) and differential pulse voltammetry (DPV)—two powerful electrochemical techniques that measure current response under applied voltages—to evaluate the sensor's performance. These methods are particularly effective for detecting electroactive molecules like isoniazid, which undergoes oxidation at specific voltages.
The experiments were conducted with isoniazid solutions of varying concentrations in a buffer solution that mimics physiological conditions. To assess real-world applicability, the researchers also tested the sensor with human plasma samples spiked with known isoniazid concentrations and compared the results with established standard methods 1 8 .
Oxidation potential shift
Linear range: 10-80 μM
Minimal interference
In human plasma
| Tool/Reagent | Function/Role | Specific Examples |
|---|---|---|
| Multi-Walled Carbon Nanotubes (MWCNTs) | Conductive backbone with high surface area; electron transfer highway | Pristine MWCNTs, carboxyl-functionalized MWCNTs 4 |
| Iron Phthalocyanine (FePc) | Electrocatalytic center; facilitates isoniazid oxidation | FePc, FePc precursors (FePc.ClO₄) 2 4 |
| Functionalization Agents | Modify CNT surfaces to enhance FePc attachment | HNO₃, H₂SO₄, ethylenediamine 4 5 |
| Electrode Materials | Sensor platform for composite immobilization | Glassy carbon electrode (GCE), screen-printed carbon electrode (SPCE) 1 3 |
| Characterization Techniques | Verify composite formation and structure | Raman spectroscopy, SEM, TEM, XPS 1 4 |
| Electrochemical Methods | Sensor performance evaluation | Cyclic Voltammetry (CV), Differential Pulse Voltammetry (DPV) 1 6 |
The development of this FePc-MWCNT nanocomposite for isoniazid detection represents a significant step forward in electrochemical sensing technology. By harnessing the unique properties of both carbon nanotubes and iron phthalocyanine, researchers have created a sensor with exceptional sensitivity, high selectivity, and proven applicability to biological samples. The synergistic combination of these materials results in a detection system that outperforms many conventional approaches.
Looking ahead, this technology holds promise for point-of-care medical testing, potentially allowing healthcare providers to monitor medication levels quickly and accurately during patient visits. The fundamental approach could also be adapted to detect other pharmaceutical compounds or biological markers by modifying the catalytic component. As research progresses, we may see these sensors incorporated into wearable devices or continuous monitoring systems that provide real-time feedback on medication levels.
The marriage of nanotechnology with electroanalytical chemistry continues to yield remarkable tools that bridge the gap between laboratory science and clinical application. The FePc-MWCNT sensor for isoniazid detection exemplifies how sophisticated materials engineering can address very practical healthcare challenges, ultimately contributing to more effective disease management and patient care.
Potential for rapid medication monitoring in clinical settings.
Future integration into continuous monitoring devices.
Adaptable platform for monitoring various pharmaceuticals.