Fluorescent Nitrogen-doped Carbon Dots-based Turn-off Sensor for Bilirubin

Bilirubin (BR), a heme protein produced from breakdown of haemoglobin is present in aged red blood cells; whose abnormal concentration is associated with diseases like hyperbilirubinemia, coronary disease, iron deficiency, and so on. Herein, we have synthesized a selective, sensitive, and low-cost sensing platform using fluorescent nitrogen doped carbon dots (NCDs), prepared from precursors; citric acid and urea via a simple microwave-assisted method. The emission at 444 nm on excitation with 360 nm was well quenched in presence of BR suggesting a direct turn-off detection for BR. Characterization of developed probe was done by UV-Visible absorption studies, photoluminescence studies, SEM, TEM, ATR-FTIR, XPS, and DLS analysis. BR was detected with a Limit of Detection (LoD) and Limit of Quantification (LoQ) of 0.32 µM and 1.08 µM respectively. NCDs exhibited excellent selectivity and sensitivity towards BR in the presence of co-existing biomolecules and ions. Practical feasibility was checked by paper-strip-based sensing of BR and spiked real human samples were used for conducting real sample analysis.

Spectral analysis with highly collimated mini-LEDs as light sources for quantitative detection of direct bilirubin

Because the human eye cannot visually detect the results of direct bilirubin test papers accurately and quantitatively, this study proposes four different highly collimated mini light-emitting diodes (HC mini-LEDs) as light sources for detection. First, different concentrations of bilirubin were oxidized to biliverdin by FeCl3 on the test paper, and pictures were obtained with a smartphone. Next, the red, green, and blue (RGB) channels of the pictures were separated to average grayscale values, and their linear relationship with the direct bilirubin concentration was analyzed to detect bilirubin on the test paper noninvasively and quantitatively. The experimental results showed that when green HC mini-LEDs were used as the light sources and image analysis was performed using the G channel, for a direct bilirubin concentration range of 0.1-2 mg/dL, the G channel determination coefficient (R2) reached 0.9523 and limit of detection was 0.459 mg/dL. The detection method proposed herein has advantages such as rapid analysis, noninvasive detection, and digitization according to RGB grayscale changes in the images of the detection test paper.

Development of antioxidant and smart NH3 -sensing packaging film by incorporating bilirubin into κ-carrageenan matrix

BACKGROUND

Active and smart food packaging based on natural polymers and pH-sensitive dyes as indicators has attracted widespread attention. In the present study, an antioxidant and amine-response color indicator film was developed by incorporating bilirubin (BIL) into the κ-carrageenan (Carr) matrix.

RESULTS

It was found that the introduction of BIL had no effect on the crystal/chemical structure, water sensitivity and mechanical performance of the Carr-based films. However, the barrier properties to light and the thermal stability were significantly improved after the addition BIL. The Carr/BIL composite films exhibited excellent 1,1-diphenyl-2-picryl-hydrazyl (i.e. DPPH)/2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (i.e. ABTS) free radical scavenging abilities and color responsiveness to different concentrations of ammonia. The application assay reflected that the Carr/BIL0.0075 film was effective in delaying the oxidative deterioration of shrimp during storage and realizing the color response of its freshness through the change of b* value.

CONCLUSION

Active and smart packaging films were successfully prepared by incorporating different contents of BIL into the Carr matrix. The present study helps to further encourage the design and development of a multi-functional packaging material. © 2023 Society of Chemical Industry.

A highly sensitive fluorescence "on-off-on" sensing platform for captopril detection based on AuNCs@ZIF-8 nanocomposite

Here, a novel fluorescent sensing strategy is established for the detection of captopril (CP) sensitively on the basis of a nanocomposite of gold nanoclusters (AuNCs) and metal-organic framework (AuNCs@ZIF-8). The aggregation-induced emission (AIE) effect will be triggered when AuNCs is encapsulated by metal-organic framework (MOF) which served as a carrier since it limits the molecular motion of AuNCs, and the fluorescence of AuNCs greatly enhanced about 5-time after forming the nanocomposites of AuNCs@ZIF-8. The strong orange-emission at 562 nm was quenched in the presence of mercury ions through dynamic quenching. After adding captopril, the quenched fluorescence of AuNCs@ZIF-8/Hg2+ system would be restored due to the specific interaction among captopril with mercury ions. Simultaneously, the restored degree of AuNCs@ZIF-8/Hg2+ fluorescence depended on the concentration of captopril. Hence, with AuNCs@ZIF-8 serving as reporter signal, the captopril content can be monitored by an "on-off-on" fluorescence sensing mode with a linear relationship of 1-100 μM, and the limit of detection for captopril was 0.134 μM.

Fluorescence detection platform of metal-organic frameworks for biomarkers

Sensitive and selective detection of biomarkers is crucial in the study and early diagnosis of diseases. With the continuous development of biosensing technologies, fluorescent biosensors based on metal-organic frameworks have attracted increasing attention in the field of biomarker detection due to the combination of the advantages of MOFs, such as high specific surface area, large porosity, and structure with tunable functionality and the technical simplicity, sensitivity and efficiency and good applicability of fluorescent detection techniques. Therefore, researchers must understand the fluorescence response mechanism of such fluorescent biosensors and their specific applications in this field. Of all biomarkers applicable to such sensors, the chemical essence of nucleic acids, proteins, amino acids, dopamine, and other small molecules account for about a quarter of the total number of studies. This review systematically elaborates on four fluorescence response mechanisms: metal-centered emission (MC), ligand-centered emission (LC), charge transfer (CT), and guest-induced luminescence change (GI), presenting their applications in the detection of nucleic acids, proteins, amino acids, dopamine, and other small molecule biomarkers. In addition, the current challenges of MOFs-based fluorescent biosensors are also discussed, and their further development prospects are concerned.

Nanomaterials for fluorescent assay of bilirubin

The accumulation of bilirubin in blood is associated with many diseases. Sensitive and accurate detection of bilirubin is of great significance for personal health care. The rapid development of fluorescent nanomaterials promotes rapid development in the bilirubin assay. In this review, traditional methods for detection of bilirubin are briefly presented to compare with fluorescent nanosensors. Subsequently, the recent progress of different types of fluorescent nanomaterials for determination of bilirubin is summarized. Further, the performance of fluorescent nanosensors and conventional techniques for sensing bilirubin are compared. To this end, the challenges and prospects concerning the topics are discussed. This review will provide some introductory knowledge for researchers to understand the status and importance of fluorescent nanosensors for sensing bilirubin.

Current and emerging technologies for the timely screening and diagnosis of neonatal jaundice

Neonatal jaundice is one of the most common clinical conditions affecting newborns. For most newborns, jaundice is harmless, however, a proportion of newborns develops severe neonatal jaundice requiring therapeutic interventions, accentuating the need to have reliable and accurate screening tools for timely recognition across different health settings. The gold standard method in diagnosing jaundice involves a blood test and requires specialized hospital-based laboratory instruments. Despite technological advancements in point-of-care laboratory medicine, there is limited accessibility of the specialized devices and sample stability in geographically remote areas. Lack of suitable testing options leads to delays in timely diagnosis and treatment of clinically significant jaundice in developed and developing countries alike. There has been an ever-increasing need for a low-cost, simple to use screening technology to improve timely diagnosis and management of neonatal jaundice. Consequently, several point-of-care (POC) devices have been developed to address this concern. This paper aims to review the literature, focusing on emerging technologies in the screening and diagnosing of neonatal jaundice. We report on the challenges associated with the existing screening tools, followed by an overview of emerging sensors currently in pre-clinical development and the emerging POC devices in clinical trials to advance the screening of neonatal jaundice. The benefits offered by emerging POC devices include their ease of use, low cost, and the accessibility of rapid response test results. However, further clinical trials are required to overcome the current limitations of the emerging POC's before their implementation in clinical settings. Hence, the need for a simple to use, low-cost POC jaundice detection technology for newborns remains an unsolved challenge globally.

A Cd(ii)-organic framework as a highly sensitive and rapid fluorometric sensor for ascorbic acid in aqueous medium

A new Cd(ii) MOF was used as a fluorometric sensor for ascorbic acid in water, fruits, vegetables and human urine.

A deoxygenation-switch-based red-emitting fluorogenic light-up probe for the detection of highly toxic free bilirubin in human blood serum

Reaction-based chemical switches are attracting great interest due to their high selectivity, and their use has become a powerful technique for developing fluorogenic probes. Herein, a benzorhodol-derivative-attached N-oxide probe (DEBNox) has been designed as a new fluorogenic probe for the detection of the biologically toxic species bilirubin based on a deoxygenation switching mechanism. Upon reaction with added Fe³⁺, bilirubin produces Fe²⁺ ions in situ, which in turn promote a deoxygenation reaction with DEBNox to generate the corresponding high-red-fluorescence (λ_em: ∼623 nm) benzorhodol derivative (DEB). This type of Fe³⁺-mediated response helps the probe to act as a qualified turn on selective fluorescence sensor for bilirubin with a detection range as low as 33 nM. Moreover, the probe was successfully employed to detect free bilirubin in human blood serum specimens with acceptable accuracy and reliability. This DEBNox-based light-up strategy also facilitates the construction of reliable and highly sensitive assays based on a paper-based strategy, similar to pH-indicator paper, as is demonstrated here via bilirubin detection in real serum samples. These findings could be useful for developing powerful diagnostic tools for the detection of free bilirubin in the near further.

Post-synthetically modified metal-organic frameworks for sensing and capture of water pollutants

Thanks to a bottom-up design of metals and organic ligands, the library of metal-organic frameworks (MOFs) has seen a conspicuous growth. Post-synthetically modified MOFs comprise a relatively smaller subset of this library. Whereas the approach of post-synthetic modification was seminally introduced for MOFs in the early 1990s, the earliest examples of post-synthetically modified MOFs are only congruous with adsorption and catalysis. The utility of PSM-derived MOFs for the sensing and capture of water contaminants is relatively niche. Arguably though, an increasing number of post-synthetically modified MOFs are finding relevance in the context of water pollutant remediation. In this article, we review the recent advances in this area and propose a structure-function relationship-guided blueprint for the future outlook.

Synthesis of Copper Metal Organic Framework Based on Schiff Base Tricarboxylate Ligand for Highly Selective and Sensitive Detection of 2,4,6-Trinitrophenol in Aqueous Medium

By using Schiff base tricarboxylate ligand 5-(4-carboxybenzylideneamino)isophthalic acid (H₃CIP), a new imine functionalized copper metal organic framework (MOF) has been synthesized solvothermally. It was fully characterized by Fourier Transform Infrared (FTIR) Spectroscopy, Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), and elemental mapping techniques. The as-synthesized MOF has been utilized as fluorescent probe for detection of nitro aromatic explosives (NAEs). The results show that the copper MOF can be developed into highly selective and sensitive sensor for detection of TNP in the aqueous medium via the "turn-off" quenching response. The linear fitting of the Stern-Volmer plot for TNP offered large quenching constant of 1.07 × 10⁴ M^-1 for Cu-MOF indicating the high sensitivity of the sensing process. Outstanding sensitivity of prepared material towards TNP detection was further validated by the low detection limit of 80 ppb (0.35 µM). The detailed mechanistic studies for their mode of action and density functional theory (DFT) calculations reveals that photo-induced electron transfer (PET) and fluorescence resonance energy transfer (FRET) processes, as well as electrostatic interactions (i.e. H-bonding) are the key factors for the turn-off response toward TNP by this fluorescent sensor. Thus, this new LMOF owing to their high water stability and remarkable functional features are potential candidates which can be developed into selective and sensitive TNP detection devices.

Mixed matrix membranes containing fluorescent coordination polymers for detecting Cr2O72- with high sensitivity, stability and recyclability

Three coordination polymers (CPs) were synthesized by using CdII, fluorescent 9,10-di(4-pyridyl)anthracene (dpa), and cyclohexane-1,4-dicarboxylic acid (H2cda), and they are [Cd2(dpa)2(cda)Cl2]n (1), [Cd(dpa)2(cda)]n (2) and [Cd(dpa)(cda)(H2O)]n (3). Both 1 and 2 are fluorescent and contain nonporous layers. 3 is an isomer of 2 and contains a porous diamondoid network. Fluorescent mixed matrix membranes were prepared by dispersing the particles of 1 or 2 within the matrix of polymethyl methacrylate, and showed high sensitivity and selectivity for detecting Cr2O72- in water. Both stability and recyclability of the MMMs were remarkably higher than those of the CP powders.

Metal-Organic Frameworks for Liquid Phase Applications

In the last two decades, metal-organic frameworks (MOFs) have attracted overwhelming attention. With readily tunable structures and functionalities, MOFs offer an unprecedentedly vast degree of design flexibility from enormous number of inorganic and organic building blocks or via postsynthetic modification to produce functional nanoporous materials. A large extent of experimental and computational studies of MOFs have been focused on gas phase applications, particularly the storage of low-carbon footprint energy carriers and the separation of CO2-containing gas mixtures. With progressive success in the synthesis of water- and solvent-resistant MOFs over the past several years, the increasingly active exploration of MOFs has been witnessed for widespread liquid phase applications such as liquid fuel purification, aromatics separation, water treatment, solvent recovery, chemical sensing, chiral separation, drug delivery, biomolecule encapsulation and separation. At this juncture, the recent experimental and computational studies are summarized herein for these multifaceted liquid phase applications to demonstrate the rapid advance in this burgeoning field. The challenges and opportunities moving from laboratory scale towards practical applications are discussed.

Aggregation-induced emission enhancement of gold nanoclusters in metal-organic frameworks for highly sensitive fluorescent detection of bilirubin

A fluorescence analysis method based on gold nanocluster (AuNC) and metal-organic framework (MOF) composite materials (AuNCs@ZIF-8) was established for highly sensitive detection of bilirubin (BR). First, AuNCs@ZIF-8 was successfully obtained by co-precipitation and displayed an aggregation-induced emission enhancement by the confinement effect of the MOFs (i.e., ZIF-8). The product showed approximately 7.0 times enhancement in the quantum yield and longer fluorescence lifetime from 2.29 μs to 11.51 μs compared with AuNCs. When BR combined with the metal node Zn2+ of ZIF-8, the skeleton of the composite was destroyed, leading to a great decrease in the fluorescence intensity by the transformation of the AuNCs from the aggregated state to dispersed state. The linear range for the detection of BR was 0.1-5.0 μM, with the limit of detection (LOD) of 0.07 μM (S/N = 3). The AuNCs@ZIF-8 exhibited a selective response toward BR within 5 min and detected BR in human serum. The long-wavelength emission by AuNCs avoided the interference of the complex biomatrix background fluorescence, indicating their great application prospects for clinical diagnosis.

Metal–organic frameworks as photoluminescent biosensing platforms: mechanisms and applications

Recent progress of MOF-based photoluminescent platforms: a comprehensive overview of their applications in biosensing and underlying mechanisms.

An acetoxy functionalized Al(III) based metal-organic framework showing selective "turn on" detection of perborate in environmental samples

Here, we have described the design, preparation and detailed characterization of a new acetoxy functionalized aluminium based metal-organic framework (MOF) called CAU-10-OCOCH3 (1) (CAU stands for Christian-Albrechts-University). The desolvated compound was employed for the detection of perborate in a pure aqueous environment. The presented MOF based perborate sensing probe (1) was synthesized by employing 5-acetoxyisophthalic acid and AlCl3·6H2O as the linker molecule and metal salt source, respectively, in DMF/H2O medium at 120 °C for 12 h. The material (1') showed a very selective fluorescent turn-on response towards perborate in aqueous medium with the coexistence of several competitive analytes. A dramatic increment (65 fold) in emission intensity of the probe was observed within 5 min of the addition of perborate. A chemo-selective reaction between perborate and the acetoxy functionality and subsequent hydrolysis of the acetoxy group to the hydroxy group is the main cause of the turn-on nature of detection. The material showed a detection limit of 1.19 μM. The probe was also applied for the recognition of perborate in several environmental water samples. The material is the first ever MOF based probe for selective detection of perborate.

Bilirubin Protects Transplanted Islets by Targeting Ferroptosis

Islet transplantation is an attractive treatment for type 1 diabetic patients. However, transplanted islets suffered from considerable cell death due to inflammatory reactions and oxidative stress. Ferroptosis is a programmed death characterized by iron-dependent lipid peroxidation, which has been implicated in the islet loss and dysfunction. Our previous studies showed that bilirubin displayed protection effect for islets by inhibiting early inflammation and oxidative stress. However, whether bilirubin protects islets by targeting ferroptosis has not yet been elucidated. Here, the isolated islet was exposed to ferroptosis-inducing agents with or without bilirubin. Islet viability, insulin secretion, and oxidative stress levels were assessed. Subsequently, the pretreated islets were transplanted into the subrenal site of streptozotocin-induced diabetic mice. Bilirubin could significantly attenuate ferroptosis in isolated islets, along with reduced oxidative stress, elevated GPX4 expression and upregulation of Nrf2/HO-1. Experimental data also confirmed that bilirubin could chelate iron. In vivo graft study demonstrated that euglycemia was achieved in diabetic mice receiving bilirubin-pretreated islets within 24 hours, while the control islets required at least 7 days. Bilirubin could improve islet viability and function through inhibiting ferroptosis, which could be of clinic interest to apply bilirubin into the islet transplantation system.

Applications of Functional Metal-Organic Frameworks in Biosensors

In recent decades, fast advancements in the fields of metal-organic frameworks (MOFs) are providing unprecedented opportunities for the development of novel functional MOFs for various biosensing applications. Exciting progress is achieved due to the combination of MOFs with various functional components, which introduces novel structures and new features to the MOFs-based biosensing applications, such as higher stability, higher sensitivity, higher flexibility, and higher specificity. This review aims to be a comprehensive summary of the most recent advances in the development of functional MOFs for various biosensing applications, placing special attention on important contributions in recent 3 years. In this review, the most recent developments in design and synthesis of functional MOFs for biosensing applications are summarized. MOFs-based biosensing applications are outlined according to the central roles of MOFs in biosensors, which include carriers of sensitive elements, enzyme-mimic elements, electrochemical signaling, optical signaling, and gas sensing. Finally, the current challenges and future development trends of functional MOFs for biosensing applications are proposed and discussed.

A selective and sensitive fluorescent probe for bilirubin in human serum based on europium(III) post-functionalized Zr(IV)-Based MOFs

In the present study, a kind of Eu(III) post-functionalized Zr(IV)-based metal-organic framework (UiO-66(COOH)₂, Zr-MOF: Eu³⁺) was synthesized and utilized as an independently luminescent probe for sensing bilirubin (BR) in human serum, a biomarker of jaundice hepatitis. It can be served as a turn-off fluorescent switch for BR because its red emission from Eu³⁺ can be easily quenched by BR through a fluorescent resonant energy transfer (FRET) process between BR and its ligands, and as a result, BR is recognized successfully. Particularly, Zr-MOF: Eu³⁺ has shown many appealing properties, such as high sensitivity, quick response (less than 1 min), broad response window (0-15 μM), and excellent selectivity. Most importantly, a kind of portable test paper based on Zr-MOF: Eu³⁺ probe has been developed for directly assessing the level of BR in real human serum and further diagnosing bilirubin-related diseases via visually observing the luminescent color variation.

Post-synthetic modification of a metal–organic framework with a chemodosimeter for the rapid detection of lethal cyanide via dual emission

A post-synthetically modified chemodosimeter grafted MOF is presented for the selective, visual and fluorogenic detection of cyanide via dual emission.

Rapid switch-on fluorescent detection of nanomolar-level hydrazine in water by a diacetoxy-functionalized MOF: application in paper strips and environmental samples

A diacetoxy-functionalized Zr-based metal–organic framework was employed for the selective, ultra-sensitive, turn-on fluorescent detection of hydrazine in an aqueous medium.

A functionalized UiO-66 MOF for turn-on fluorescence sensing of superoxide in water and efficient catalysis for Knoevenagel condensation

A MOF based sensor is reported for specific, rapid, and sensitive sensing of O₂^·− and effective and recyclable catalysis of Knoevenagel condensation.