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Rapid interest in identifying specific biomarkers has been sparked by the development of wearable electrochemical sensors for physiological and biological monitoring via noninvasive measurement. During anaerobic metabolic circumstances, monitoring the lactate content become critical for noninvasive diagnostic of hypoxia. To improve the sensitivity of wearable sweat biosensors for detecting lactate concentrations, in this study, metal–organic framework (MOF)-derived NiCo-based layered double hydroxides (m-NiCo LDHs) with N-doped graphene quantum dots (NGQDs) decoration are designed. According to the X-ray absorption spectroscopy (XAS) analysis, the incorporation of NGQDs will alter the local electronic structure of transition metals in m-NiCo LDHs, thereby reducing the charge transfer resistance and accelerating the electron transfer kinetics during electrochemical reactions of lactate detection. After understanding the role of NGQDs in the matrix of m-NiCo LDHs, as-designed NGQD/m-NiCo LDH-based electrochemical biosensors for lactate detection displayed superior sensitivity of 62.63 ± 1.50 μA mM–1 cm–2 under an applied potential of 0.60 V (vs Ag/AgCl/3 M KCl) with the lactate concentration range of 0 to 15 mM in alkaline condition, compared to pristine NiCo LDH (16.77 ± 1.70 μA mM–1 cm–2)- and m-NiCo LDH (45.45 ± 4.39 μA mM–1 cm–2)-based ones. This research provides a potential electrocatalyst of GQD-modified MOF-derived LDHs for using enzyme-free electrochemical lactate sensors with reliable and stable performance in order to implement noninvasive human perspiration monitoring on wearable bioelectronics. [ABSTRACT FROM AUTHOR]

Emerging wearable devices with noninvasive biosensing technologies have sparked substantial interest for constant monitoring of substances in bodily fluids, which might be used to detect human health issues. Uric acid (UA) is a crucial indicator of a high relationship with gout, hyperuricemia, and Lesch–Nyhan syndrome. Therefore, developing a wearable device to noninvasively monitor the UA levels in sweat has drawn enormous attention. In this work, boron-doped graphene quantum dots anchored to carbon nanotubes (BGQDs/CNTs) were proposed as noble-metal-free electrocatalysts for the design of the enzyme-free wearable sensors to monitor the concentration of UA in human sweat. BGQDs could provide extra active sites to enhance the electrocatalytic ability of the UA oxidation reaction. From the results, BGQDs/CNTs exhibit ultrahigh sensitivity of 8.92 ± 0.22 μA μM–1 cm–2 for UA detection compared to pristine CNTs (4.24 ± 0.24 μA μM–1 cm–2). Moreover, density functional theory calculations indicate that B atoms can strengthen the UA molecule adsorption and enlarge electron transfer from the UA molecule to the B-doped graphene sheet, supporting the high sensitivity of BGQDs for UA detection. Hence, this study offers a promising electrocatalyst for using an enzyme-free electrochemical UA sensor with a dependable and steady performance to further the use of wearable electronics. [ABSTRACT FROM AUTHOR]

[Display omitted] High energy resource demand has led to the rapid development of hydrogen as a clean fuel through electrolytic water splitting. The exploration of high-performance and cost-effective electrocatalysts for water splitting is a challenging task to obtain renewable and clean energy. However, the sluggish kinetics of oxygen evolution reaction (OER) greatly hindered its application. Herein, a novel oxygen plasma-treated graphene quantum dots embedded Ni-Fe Prussian blue analogue (O-GQD-NiFe PBA) is proposed as a highly active electrocatalysts for OER. Furthermore, the defect induced by GQD can provide an abundant lattice mismatch in the matrix of NiFe PBA, which further facilitates faster electron transport and kinetic performance. After optimization, the as-assembled O-GQD-NiFe PBA exhibits excellent electrocatalytic performance towards OER with a low overpotential of 259 mV for reaching a current density of 10 mA cm−2 and impressive long-term stability for 100 h in an alkaline solution. This work broadens the scope of metal–organic frameworks (MOF) and high-functioning carbon composite as an active material for energy conversion systems. [ABSTRACT FROM AUTHOR]

Addressing energy and environmental issues, developing highly efficient, durable, and earth-abundant, electrocatalysts are crucial in oxygen evolution reaction (OER) for energy conversion and storage. Extensive research about the metal-organic framework (MOF) derived layered double hydroxides (LDH) and carbon-based electrocatalysts have been devoted, despite the exceptional performance in OER, yet the limited exposed active sites remain a challenge. Therefore, we reported a novel heteroatom-doped graphene quantum dots (GQDs) incorporated into MOF-derived NiFe-LDH. Taking advantage of abundant active and edge sites of GQDs and modifying the surface chemistry by chemical doping with foreign atoms, the designed heteroatom-doped GQDs/MOF-derived LDH exhibited superior catalytic performance low overpotential of 251 mV at a current density of 100 mA cm−2 in alkaline media. Our result confirmed the synergistic effect between the doped heteroatom and the uttermost exposure of heteroatom-doped GQDs/MOF-derived LDH's active sites on its surface, providing swift reactant's transportation and adequate contact for improving the OER performance. [Display omitted] • A novel hybrid heteroatom-doped GQDs/MOF-derived LDH electrocatalyst has been developed. • The relationship between single and dual-doped GQDs in OER activity has been explored and optimized. • Synergistic effect of N and B dopants within GQDs significantly improves the OER performance. • B,N-GQDs/MOF-derived NiFe LDH exhibits superior electrocatalytic OER performance (η 100 = 251 mV). [ABSTRACT FROM AUTHOR]

[Display omitted] • A precisely engineered molecular Fe site were proposed, –a breakthrough in the catalysis design. • The molecularly well-defined Fe sites were successfully immobilized onto the GQDs matrix. • The pioneering strategy of molecular Fe immobilization on the OER kinetic intricacies were explored. • The well dispersed molecular Fe sites on the GQDs matrices demonstrated not only an outstanding OER features, but also stability. The emergence of efficient electrocatalysts to facilitate the thermodynamically demanding and kinetically challenging oxygen evolution process (OER), which includes the coordinated transfer of four protons and four electrons, remains an issue. The effective transfer of energy encourages molecular-level control over key redox transitions involving small-molecule substrates (O 2 , and H 2 O), at or near electrode surfaces. While many molecular catalysts have been shown highly active for OER, immobilizing those onto the heterogenous solid matrices is challenging. Herein, graphene quantum dots (GQDs), a carbonaceous sub-class, was used as the solid matrices to conjugate the molecular catalyst onto its surface owing to its high surface area and electronic conductivity. Through the coordinated environment of the conjugated material, the molecular Fe sites on the GQDs surface exhibited outstanding OER features, achieving an ultra-low overpotential of 223 mV and 241 mV at a current density of 50 and 100 and mA/cm2, respectively, and excellent stability over 24 h. Our results marked a pioneering step in that through conjugation, these molecular sites were well dispersed at the GQDs matrices and were intrinsically active for OER. [ABSTRACT FROM AUTHOR]

Dissolved oxygen (DO) is an essential indicator for evaluating water quality, the exquisitely sensitive electrochemical DO sensor could accurately record response which was based on oxygen reduction reaction (ORR) with a sluggish reaction rate. Thus, high-efficient ORR electrocatalysts are urgently needed for broad applications. As a matter of fact, graphene quantum dots (GQDs) have attracted a great deal of attention, several heteroatoms are extensively introduced in GQDs fragments to regulate their inherent chemical and electrical properties by adjusting their electronic structure. However, B–N–C moieties always exist for some BN-codoped carbons due to the intermolecular force that might prohibit its electrocatalytic activity. Therefore, this research design a strategy to solve this problem; despite substantial efforts, this study shows a metal-free B-doped GQD/N-doped carbon nanotubes (BGQD/NCNTs) electrode significantly influences ORR electrocatalytic activity due to the synergistic effect and abundant active sites. Herein, BGQD/NCNTs exhibit an excellent ORR performance with an onset potential of 0.91 V (vs. RHE), exceeding most reported GQDs-introduced electrocatalysts; it also outperformed the commercial electrocatalyst in terms of long-term stability. For seawater DO sensing, BGQD/NCNTs exhibit ultra-high sensitivity of 0.011 mA/cm2ppm and further integrate into an online detection platform to accomplish the aim of continuous monitoring via a wireless connection. [Display omitted] • A novel strategy to lower B–N moieties in B,N-codoped carbon based electrocatalyst was proposed. • BGQDs/NCNTs display better onset potential toward ORR than pristine CNTs. • BGQD/NCNTs shows promising sensitivity and stability for dissolved oxygen sensing in seawater. • The aim of continuous online monitoring was achieved via a wireless connection. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel surface engineering strategy via GQD-assistance electrocatalysts has been established. • The metal activation by GQD through the higher transition metal interaction was explored. • Synergistic interaction of F ions and GQD on PBA matrix significantly enhances the OER performance. • GQD/F-NiFe PBA exhibits better electrocatalytic OER performance of 318 mV at 50 mA cm−2. Electrolytic water splitting for hydrogen has rapidly developed along with the increasing necessity for clean energy resources. Meanwhile, the obstacle originating from the slow 4-electron-involved oxygen evolution reaction (OER) pushes the urgency to create efficient, durable, earth-abundant electrocatalysts. As one of the promising candidates, it remains a challenge to enhance the reactivity of the Prussian-blue analogue (PBA) towards the OER. Herein, we propose a unique tandem surface reconstruction strategy for NiFe PBA followed by heteroatomic F doping and graphene quantum dot (GQD) decoration to modify the surface chemistry. GQD could improve electrocatalytic performance through the higher transition metal interaction with NiFe PBA due to the distinct electronic structures and an abundance of edge sites. X-ray absorption spectroscopy (XAS) revealed that F- ions were more likely to affect metal bonds. In contrast, GQD plays a role in modifying the metal states through the higher transition metal interaction. The proposed GQD/F-NiFe PBA with tandem surface engineering demonstrated promising electrocatalytic activity for OER in an alkaline medium, with an overpotential of 318 mV at a current density of 50 mA cm−2 and a small Tafel slope of 34.7 mV dec-1. The proposed tandem surface engineering for modifying PBA-based material surfaces represents a novel approach to designing advanced electrocatalysts. [ABSTRACT FROM AUTHOR]

Understanding the levels change in biomarkers over time, especially glucose, is crucial for diabetics to inform early therapy. Recently, wearable sweat biosensors which operate in a non-invasive way have raised attention, providing continuous monitoring of the severity level. Nevertheless, the key challenges are that multiplexed motions may result in undesirable metal cracking by the rigid electrocatalytic layer, leading to decreased sensitivity and stability. In this work, we designed an N-GQDs anchored PANI matrix to realize flexible wearable biosensors with high detection accuracy. Upon the enhanced electron transfer by N-GQDs, N-GQDs/PANI nanocomposite offers greater sensitivity in H 2 O 2 detection compared to pristine PANI, resulting in a sensitivity of 68.1 ± 1.11 and 44.06 ± 2.1 μA mM−1 cm−2, respectively. Moreover, after the glucose oxidase (GOx) immobilization, GOx/N-GQDs/PANI-based biosensors had shown excellent performance for glucose detection in artificial sweat. Precise glucose detection was also maintained after integrating into a flexible electrode, the sensitivity of the GOx/N-GQDs/PANI-based biosensor had retained 93.2 % with no apparent cracks in the morphology of the nanocomposite layer, compared to GOx/Pt-based one (71.3 %) toward glucose detection after a continuous bending test. Thus, the N-GQDs/PANI nanocomposite layer can provide reliable long-term monitoring with robust electrodes for non-invasive human sweat glucose monitoring on a wearable biosensor. [Display omitted] • A novel developed nanocomposite layer of N-GQDs/PANI was proposed. • The relationship between the N doping levels of N-GQDs and PANI toward H 2 O 2 detection has explored. • The N-GQDs modified PANI successfully lowered the charge transfer resistance. • GOx/N-GQDs/PANI can maintain its excellent sensitivity under continuous bending test. [ABSTRACT FROM AUTHOR]