Morphology Control Strategy of Bimetallic MOF Nanosheets for Upgrading the Sensitivity of Noninvasive Glucose Detection

Surface engineered metal-organic framework-based electrochemical biosensors for enzyme-mimic ultrasensitive detection of glucose: recent advancements and future perspectives

Metal-Organic Frameworks (MOFs) have garnered significant attention in the development of electrochemical glucose sensors due to their unique and advantageous properties. The highly tunable pore channels of MOFs facilitate optimal diffusion of glucose molecules, while their large specific surface area provides abundant active sites for electrochemical reactions. Furthermore, the well-dispersed metallic active sites within MOFs enhance electrocatalytic activity, thereby improving the sensitivity and selectivity of glucose detection. These features make MOF-based nanoarchitectures promising candidates for the development of efficient and sensitive glucose sensors, which are crucial for diabetes management and monitoring. The integration of enzymatic biosensors with nanotechnology continues to drive advancements in glucose monitoring, offering the potential for more accurate, convenient, and user-friendly tools for diabetes management. Current research explores non-invasive glucose monitoring methods, such as using sweat, saliva, or interstitial fluid instead of blood, aiming to reduce the discomfort and inconvenience associated with frequent blood sampling. A review of the advancements and applications of MOF-based enzyme-mimic electrochemical sensors for glucose monitoring can provide valuable insights for young researchers, inspiring future research in biomedical device fabrication. Such reviews not only offer a comprehensive understanding of the current state of the art but also highlight existing challenges and future opportunities in the field of enzyme-less glucose sensing, particularly in the surface modification techniques of highly porous MOFs. This fosters innovation and new research directions. By understanding the advantages, challenges, and opportunities, researchers can contribute to the development of more effective and innovative enzyme-mimic glucose sensing transducers, which are essential for advancing biomedical devices.

A wearable non-enzymatic sensor for continuous monitoring of glucose in human sweat

To enhance personalized diabetes management, there is a critical need for non-invasive wearable electrochemical sensors made from flexible materials to enable continuous monitoring of sweat glucose levels. The main challenge lies in developing glucose sensors with superior electrochemical characteristics and high adaptability. Herein, we present a wearable sensor for non-enzymatic electrochemical glucose analysis. The sensor was synthesized using hydrothermal and one-pot preparation methods, incorporating gold nanoparticles (AuNPs) functionalized onto aminated multi-walled carbon nanotubes (AMWCNTs) as an efficient catalyst, and crosslinked with carboxylated styrene butadiene rubber (XSBR) and PEDOT:PSS. The sensors were then integrated onto screen-printed electrodes (SPEs) to create flexible glucose sensors (XSBR-PEDOT:PSS-AMWCNTs/AuNPs/SPE). Operating under neutral conditions, the sensor exhibits a linear range of 50 μmol/L to 600 μmol/L, with a limit of detection limit of 3.2 μmol/L (S/N = 3), enabling the detection of minute glucose concentrations. The flexible glucose sensor maintains functionality after 500 repetitions of bending at a 180° angle, without significant degradation in performance. Furthermore, the sensor exhibits exceptional stability, repeatability, and resistance to interference. Importantly, we successfully monitored changes in sweat glucose levels by applying screen-printed electrodes to human skin, with results consistent with normal physiological blood glucose fluctuations. This study details the fabrication of a wearable sensor characterized by ease of manufacture, remarkable flexibility, high sensitivity, and adaptability for non-invasive blood glucose monitoring through non-enzymatic electrochemical analysis. Thus, this streamlined fabrication process presents a novel approach for non-invasive, real-time blood glucose level monitoring.

Shifting paradigm in electrochemical biosensing matrices comprising metal organic frameworks and their composites in disease diagnosis

Metal Organic Frameworks (MOFs) are an evolving category of crystalline microporous materials that have grabbed the research interest for quite some time due to their admirable physio-chemical properties and easy fabrication methods. Their enormous surface area can be a working ground for innumerable molecular adhesions and site for potential sensor matrices. They have been explored in the last decade for incorporation in electrochemical sensor matrices as diagnostic solutions for a plethora of diseases. This review emphasizes on some of the recent advancements in the area of MOF-based electrochemical biosensors with focus on various important diseases and their significance in upgrading the sensor performance. It summarizes MOF-based biosensors for monitoring biomarkers relevant to diabetes, viral and bacterial sepsis infections, neurological disorders, cardiovascular diseases, and cancer in a wide range of real matrices. The discussion has been supplemented with extensive tables elaborating recent trends in the field of MOF-composite probe fabrication strategies with their respective sensing parameters. The article sums up the future scope of these materials in the field of biosensors and enlightens the reader with recent trends for future research scope. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > Diagnostic Nanodevices.

Spin Crossover and Exchange Effects on Oxygen Evolution Reaction Catalyzed by Bimetallic Metal Organic Frameworks

Bimetallic metal-organic frameworks (BMOFs) have shown a superior oxygen evolution reaction (OER) performance, attributed to the synergistic effects of dual metal sites. However, the significant role of these dual-metal synergies in the OER is not yet fully understood. In this study, we employed density functional theory to systematically investigate the OER performance of NiAl- and NiFe-based BMOFs by examining all possible spin states of each intermediate across diverse external potentials and pH environments. We found that the spin state featuring a shallow hole trap state and Ni ions with a higher oxidation state serve as strong oxidizing agents, promoting the OER. An external potential-induced spin crossover was observed in each intermediate, resulting in significant changes in the overall reaction and activation energies due to altered energy levels. Combining the constant potential method and the electrochemical nudged elastic band method, we mapped the minimum free energy barriers of the OER under varied external potential and pH by considering the spin crossover effect for both NiAl and NiFe BMOFs. The results showed that NiFe exhibits better OER thermodynamics and kinetics, which is in good agreement with experimentally measured OER polarization curves and Tafel plots. Moreover, we found that the improved OER kinetics of NiFe not only is attributed to lower barriers but also is a result of improved electrical conductivity arising from the synergistic effects of Ni-Fe dual-metal sites. Specifically, replacing the second metal Al with Fe leads to two significant outcomes: a reduction in both the band gap and the effective hole mass compared to NiAl, and the initiation of super- and double-exchange interactions within the Ni-F-Fe chain, thereby enhancing electron transfer and hopping and leading to the improved OER kinetics.

Morphology Control of Zr-Based Luminescent Metal-Organic Frameworks for Aflatoxin B1 Detection

Metal-organic frameworks (MOFs) have gained significant prominence as sensing materials owing to their unique properties. However, understanding the correlation between the morphology, properties, and sensing performance in these MOF-based sensors remains a challenge, limiting their applications and potential for improvement. In this study, Zr-MOF was chosen as an ideal model to explore the impact of the MOF morphology on the sensing performance, given its remarkable stability and structural variability. Three luminescent MOFs (namely rod-like Zr-LMOF, prismoid-like Zr-LMOF, and ellipsoid-like Zr-LMOF) were synthesized by adjusting the quantities of the benzoic acid and the reaction time. More importantly, the sensing performance of these Zr-LMOFs in response to aflatoxin B1 (AFB1) was thoroughly examined. Notably, the ellipsoid-like Zr-LMOF exhibited significantly higher sensitivity compared to other Zr-LMOFs, attributed to its large specific surface area and pore volume. Additionally, an in-depth investigation into the detection mechanism of AFB1 by Zr-LMOFs was conducted. Building upon these insights, a ratiometric fluorescence sensor was developed by coordinating Eu3+ with ellipsoid-like Zr-LMOF, achieving a remarkably lower detection limit of 2.82 nM for AFB1. This study contributes to an improved comprehension of the relationship between the MOF morphology and the sensing characteristics while presenting an effective approach for AFB1 detection.

Bottom-Up Construction of Rhombic Lamellar CoNi-MOFs for the Electrochemical Sensing of H2S

Lamellar metal-organic frameworks (MOFs) have attracted significant attention in the field of electrochemical sensing due to their abundant open active sites and specific electron conductivity. Herein, by employing a bottom-up synthesis strategy, rhombic lamellar heterometallic CoNi-MOFs with varying thicknesses are constructed. This is achieved by using 4-methylpyridine as a capping agent based on the (4,6)-linked Co2(azpy)2(bptc) (azpy = 4,4'-azopyridine, bptc = 3,3',5,5'-biphenyltetracarboxylic acid) structure with a fsc topology and by introducing Ni species simultaneously. To mitigate sulfur deposition on electrodes, the triple pulse amperometry (TPA) method is employed. Among the synthesized lamellar CoNi-MOFs, lamellar CoNi-MOF-3 with the minimum thickness exhibits an optimal electrochemical sensing performance toward hydrogen sulfide, with a sensitivity of 119.3 μA·mM-1·cm-2 in the linear range of 2-2000 μM. This study pioneers a new approach to the controlled construction and electrochemical activity modification of lamellar MOF materials.

Fast and In-Depth Reconstruction of Two-Dimension Cobalt-Based Zeolitic Imidazolate Framework in Glucose Oxidation Processes

Currently, metal-organic frameworks (MOFs) have emerged as viable candidates for enduring electrode materials in nonenzyme glucose sensing. However, given the inherent water susceptibility of MOFs and their complete self-reconstruction during the process of electrochemical oxygen evolution in alkaline conditions, we are motivated to explore the truth of MOFs catalyzing glucose oxidation. In this work, we fabricated a two-dimensional cobalt-based zeolitic imidazolate framework (ZIF-L) as the electrode material for catalyzing glucose oxidation in alkaline conditions. Our explorations revealed that while the initial glucose catalytic response varied among ZIF-L samples with differing thicknesses, the ultimate steady-state catalytic performance remained largely consistent. This phenomenon arose from the transformation of ZIF-L with distinct thicknesses into CoOOH with uniform morphological and structural characteristics during the glucose catalysis process. And in situ Raman spectroscopy elucidated the sustained equilibrium within the glucose catalytic system, wherein the dynamic interconversion between CoOOH and Co(OH)2 governs the overall process. This study contributes to an enhanced understanding of the glucose catalytic mechanism aspects of nonenzymatic glucose sensor electrode materials, offering insights that serve as inspiration for the development of advanced glucose electrode materials.

A portable sensor for glucose detection in Huangshui based on blossom-shaped bimetallic organic framework loaded with silver nanoparticles combined with machine learning

In this work, we propose a blossom-like Ni, Co bimetallic metal-organic framework (NiCo-MOF) synthesized hydrothermally and decorated with silver nanoparticles (AgNPs) via chemical reduction for electrochemical enzyme-free glucose sensing. The NiCo-MOF nanostructures had large specific surface area and good sensing performance. The AgNPs enhanced the electrochemical performance of the MOF, resulting in excellent electrochemical activity. The sensor exhibited sensitivities of 1191.84 and 271.19 μA mM-1 cm-2 in the linear ranges of 0.005-1.125 and 1.525-5.325 mM, respectively, with a detection limit of 2.3 μM. The sensor was successfully applied for glucose determination in Huangshui (HS) using an artificial neural network as machine learning (ML) model. The R2 value near 1, low RMSE, and high RPD values of the proposed ML model demonstrate its excellent fitting and prediction performance. This will provide a fast and portable intelligent sensing analysis technology for the detection of glucose in HS.

Integration of Triphenylene-Based Conductive Metal-Organic Frameworks into Carbon Nanotube Electrodes for Boosting Nonenzymatic Glucose Sensing

The rational design and preparation of conductive metal-organic frameworks (MOFs) are alluring and challenging pathways to develop active catalysts toward electrocatalytic glucose oxidation. The hybridization of conductive MOFs with carbon nanotubes (CNTs) in the form of a composite can greatly improve the electrocatalytic performance. Herein, a facile one-step synthetic strategy is utilized to fabricate a Ni3(HHTP)2/CNT (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) composite for nonenzymatic detection of glucose in an alkaline solution. The Ni3(HHTP)2/CNT composite, as an electrochemical glucose sensor material, exhibits superior electrocatalytic activity toward glucose oxidation with a wide detection range of up to 3.9 mM, a low detection limit of 4.1 μM (signal/noise = 3), a fast amperometric response time of <2 s, and a high sensitivity of 4774 μA mM-1 cm-2, surpassing the performance of some recently reported nonenzymatic transition-metal-based glucose sensors. In addition, the composite sensor also shows outstanding selectivity, robust long-term electrochemical stability, favorable anti-interference properties, and good reproducibility. This work displays the effectiveness of enhancing the electrocatalytic performance toward glucose detection by combing conductive MOFs with CNTs, thereby opening up an applicable and encouraging approach for the design of advanced nonenzymatic glucose sensors.

Focus Review on Nanomaterial-Based Electrochemical Sensing of Glucose for Health Applications

Diabetes management can be considered the first paradigm of modern personalized medicine. An overview of the most relevant advancements in glucose sensing achieved in the last 5 years is presented. In particular, devices exploiting both consolidated and innovative electrochemical sensing strategies, based on nanomaterials, have been described, taking into account their performances, advantages and limitations, when applied for the glucose analysis in blood and serum samples, urine, as well as in less conventional biological fluids. The routine measurement is still largely based on the finger-pricking method, which is usually considered unpleasant. In alternative, glucose continuous monitoring relies on electrochemical sensing in the interstitial fluid, using implanted electrodes. Due to the invasive nature of such devices, further investigations have been carried out in order to develop less invasive sensors that can operate in sweat, tears or wound exudates. Thanks to their unique features, nanomaterials have been successfully applied for the development of both enzymatic and non-enzymatic glucose sensors, which are compliant with the specific needs of the most advanced applications, such as flexible and deformable systems capable of conforming to skin or eyes, in order to produce reliable medical devices operating at the point of care.

Magnetically and Electrically Responsive Soft Actuator Derived from Ferromagnetic Bimetallic Organic Framework

The advancement in smart devices and soft robotics necessitates the use of multiresponsive soft actuators with high actuation stroke and stable reversibility for their use in real-world applications. Here, this work reports a magnetically and electrically dual responsive soft actuator based on neodymium and iron bimetallic organic frameworks (NdFeMOFs@700). The ferromagnetic NdFeMOFs@700 exhibits a porous carbon structure with excellent magnetization saturation (166.96 emu g^-1 ) which allows its application to a dual functional material in both magnetoactive and electro-ionic actuations. The electro-ionic soft actuator, which is fabricated using NdFeMOFs@700 and PEDOT-PSS, demonstrates 4.5 times higher ionic charge storage capacity (68.21 mF cm^-2 ) and has excellent cycle stability compared with the PEDOT-PSS based actuator. Under a low sinusoidal input voltage of 1 V, the dual-responsive actuator displays bending displacement of 15.46 mm and also generates deflection of 10 mm at 50 mT. Present results show that the ferromagnetic bimetallic organic frameworks can open a new way to make dual responsive soft actuators due to the hierarchically porous structures with its high redox activity, superior magnetic properties, and larger electrochemical capacitance. With the NdFeMOFs@700 based soft actuators, walking movement of a starfish robot is demonstrated by applying both the magnetic and electric fields.

A sensitive enzyme-free electrochemical sensor based on a rod-shaped bimetallic MOF anchored on graphene oxide nanosheets for determination of glucose in huangshui

In this work, we propose a bimetallic Ni-Co based MOF attached to graphene oxide (GO) by a one-step hydrothermal approach which may be employed as an electrochemical enzyme-free glucose sensor. Due to the obvious synergistic catalysis of Ni and Co, as well as the combination of NiCo-MOF and GO, NiCo-MOF/GO not only enhances energy transfer and electrocatalytic performance but also provides a larger surface area and more active sites. Electrochemical studies show that NiCo-MOF/GO exhibits outstanding electrochemical activity, with a sensitivity of 11 177 μA mM^-1 cm^-2 and 4492 μA mM^-1 cm^-2 in the linear ranges of 1-497 μM and 597-3997 μM, a detection limit of 0.23 μM, and a response time of 2 seconds. More importantly, the newly fabricated sensor is successfully applied for glucose determination in huangshui. This method provides a novel strategy for the controlled fermentation process and product quality of Chinese baijiu.