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.

A ratiometric bilirubin sensor based on a fluorescent gold nanocluster film with dual emissions

Bilirubin originates from hemoglobin metabolism and is an important biomarker for liver function. A ratiometric film sensor based on gold nanoclusters (AuNCs) was fabricated for highly sensitive determination of free bilirubin (fBR). Using bovine serum albumin (BSA) as a template, AuNCs that can emit blue and red fluorescence were prepared by the hydrothermal method at different pH values. Two kinds of AuNCs were incorporated into a single film by the layer-by-layer assembly (LBL) technique. The obtained thin-film showed dual fluorescence peaks excited at 372 nm, corresponding to the blue (443 nm) and red (622 nm) emissions of AuNCs respectively. When fBR interacted with the film, both fluorescence peaks were quenched at different degrees. A ratiometric method for fBR detection was established based on the fluorescence intensity ratio of the two emissions. The linear calibration curve for fBR lay in the concentration range of 0.01-2.00 μmol L^-1 with a detection limit of 8.90 ± 0.34 nmol L^-1 (S/N = 3). The film sensor showed a quick and sensitive response to fBR and could detect fBR in real samples with satisfactory results.

Newborns bilirubin concentration determined by different methods in relation to hematocrit and albumin level

Background

Monitoring of bilirubin is essential during early neonatal life. Bilirubin in high concentration is toxic to the brain and might cause irreversible neurological damage. Several different methods for bilirubin determination are available nowadays, but inconsistent results may be obtained. The study aimed to compare dry chemistry methods with vanadate oxidation method for bilirubin determination in relation to hematocrit and albumin level in neonates and infants.

Methods

The study included 98 consecutive serum samples from newborns and infants (47 boys and 51 girls, mean age 19 ± 15 days) treated in the University Children's Hospital in Krakow. Total bilirubin (TBil) and neonatal bilirubin (NBil) concentration were measured by dry chemistry analyser (Vitros 4600, Ortho Clinical Diagnostics Inc.). Total bilirubin (TBil_V) was also measured using vanadate oxidation method (Cormay, Poland). Albumin concentration and blood morphology have been routinely determined in all children.

Results

No significant differences between the mean value of NBil (69.00 ± 67.76 μmol/L), TBil (81.26 ± 70.13 μmol/L) and TBilV (75.90 ± 60.62 μmol/L) were noticed. High coefficient correlation between NBil and TBil as well as between NBil and TBil_V were noticed (Pearson's analysis, r = 0.99, r = 0.97, respectively; p < 0.0001 in both cases). There was a positive correlation between the difference (TBil_V - NBil) and hematocrit (p < 0.009, r = 0.2664).

Conclusions

In newborns and infants the same method for bilirubin determination should be used when the concentration of bilirubin is monitored. When using vanadate oxidation method for bilirubin determination, hematocrit value should be taken into account when results are interpreted.

A Gold Nanoclusters Film Supported on Polydopamine for Fluorescent Sensing of Free Bilirubin

Serum bilirubin is an important biomarker for the diagnosis of various types of liver diseases and blood disorders. A polydopamine/gold nanoclusters composite film was fabricated for the fluorescent sensing of free bilirubin. Bovine serum albumin (BSA)-stabilized gold nanoclusters (AuNCs) were used as probes for biorecognition. The polydopamine film was utilized as an adhesion layer for immobilization of AuNCs. When the composite film was exposed to free bilirubin, due to the complex that was formed between BSA and free bilirubin, the fluorescence intensity of the composite film was gradually weakened as the bilirubin concentration increased. The fluorescence quenching ratio (F₀/F) was linearly proportional to free bilirubin over the concentration range of 0.8~50 μmol/L with a limit of detection of 0.61 ± 0.12 μmol/L (S/N = 3). The response was quick, the film was recyclable, and common ingredients in human serum did not interfere with the detection of free bilirubin.

Glucuronidated bilirubin: Significantly increased in hepatic encephalopathy

Bilirubin is produced by the breakdown of hemoglobin in senescent erythrocytes by macrophages and carried by albumin from blood circulation to the liver for removal in normal physiology. Glucuronic acid modification of bilirubin by UDP-glucuronyltransferase in the liver is the key event for its subsequent elimination from human body. Conditions that accelerate the breakdown of erythrocytes may cause an elevated blood level of unconjugated bilirubin whereas the factors affect the glucuronidated bilirubin formation and subsequent elimination may cause decreased or increased blood level of glucuronidated bilirubin, the water soluble "direct bilirubin" measured by clinical blood test. Studies showed that increased total serum bilirubin has a protective effect on cardiovascular and other related diseases, but it is unknown how direct bilirubin levels were related to different diseases. By taking advantage of the data collected in the clinical laboratory of our hospital, the direct bilirubin data from 192,535 patients with 72 clinically defined diseases were compared to that of healthy controls (10,497). Based on the mean, median, and p values, we found that patients with hepatic encephalopathy had the highest serum direct bilirubin level, which resembled acute hepatic encephalopathy caused by increased serum direct bilirubin level in neonates. In contrast, patients with uremia, nephrotic syndrome, and preeclampsia had significantly lower levels of serum direct bilirubin. Taken together, our data revealed that serum direct bilirubin levels were either increased or decreased in a disease-dependent manner. The possible molecular mechanisms of increased direct bilirubin levels in patients suffering hepatic encephalopathy are discussed.

Efficient detection of a biomarker for infant jaundice by a europium(iii)-organic framework luminescence sensor

Efficient detection of excess bilirubin in human serum and urine is highly important for the early diagnosis of infant jaundice. A highly stable Eu(iii)-based microporous framework with bent {Eu(COO)} chains interconnected by pairs of T-shaped 4,4′-(4,4′-bipyridine-2,6-diyl)dibenzoate (bpydb²⁻) linkers, {[Eu(H₂O)(HCOO)(bpydb)]·solvent}_n (1), was solvothermally synthesized and used as a chemical sensor for bilirubin response under clinically-applicable visible-light excitation. Due to the significant synergetic effect of the inner filter effect and photoinduced electron transfer, 1 can effectively probe trace amounts of bilirubin in aqueous solution through fluorescence decay with a strong quenching constant of 6.40 × 10⁴ M⁻¹ and low detection limit of 1.75 μM. More importantly, a portable test paper made from 1 was further developed to achieve qualitative, naked-eye visualized differentiation for the biomarker in clinical applications. These interesting findings highlight the importance of the π-conjugated antenna ligand for clinically applicable Ln-MOF sensors.

A Eu(iii)–MOF sensor with intense red luminescence can effectively probe bilirubin in water through fluorescence decay, and can be fabricated into portable test papers to achieve visualized detection of bilirubin.

A pH-Controlled Kit for Total and Direct Bilirubin Built on Mimetic Peroxidase CoFe2O4-DOPA-Catalyzed Fluorescence Enhancement

Facile and reliable detection of total bilirubin (Bt, summation of indirect and direct bilirubin) and direct bilirubin (Bd) in human serum is of crucial importance to clinical diagnosis. However, it is still a challenge to explore an ideal recognition system for discriminating Bd and indirect bilirubin (Bi). In this work, a dual-functional sensor for Bt and Bd was first built on pH-controlled and mimetic peroxidase-catalyzed fluorescence enhancement. The fluorescence of nitrogen-doped graphene quantum dots (NGQDs) can be effectively quenched by bilirubin through the IFE process. With the catalysis of dopamine-derived magnetic ferrite nanoparticles (CoFe₂O₄-DOPA), both Bd and Bi were oxidized by H₂O₂ to colorless and fluorescent oxidates at pH 8.0. Interestingly, only Bd was oxidized at pH 3.5. The discriminating principle of Bd and Bi relied on their pH-controlled oxidation potentials. A sensitive sensor for Bt and Bd was developed on the enhanced fluorescence of the NGQDs/CoFe₂O₄-DOPA/H₂O₂ sensing system after bilirubin oxidation, which was originated from a combination of the fluorescence recovery of NGQDs and newly spawned fluorescence of bilirubin oxidates. The designed probe well quantifies Bt and Bd with the detection limits of 10 and 50 nM, respectively. Moreover, a portable diagnostic kit was fabricated and successfully used for the detection of Bt and Bd in 60 unrelated human serum samples, and the obtained results were almost consistent with those measured by biochemistry analyzer. The present kit exhibits the superiorities of high sensitivity and stability, interference-resistant, and green reagents, making it a promising candidate for bilirubin detection in the clinical diagnosis of jaundice.

Development of new methods for determination of bilirubin

The ever-increasing demand for a sensitive, rapid and reliable method for determination of serum bilirubin level has been inciting the interest of the researchers to develop new methods for both laboratory set up and point of care applications. These efforts embrace measurement of different forms of bilirubin, such as, unconjugated (free and albumin bound) bilirubin, conjugated (direct) bilirubin, and total (both conjugated and unconjugated) bilirubin in the serum that may provide critical information useful for diagnosis of many diseases and metabolic disorders. Herein, an effort has been made to provide a broad overview on the subject starting from the conventional spectroscopy based analytical methods widely practiced in the laboratory setup along with the sophisticated instrument based sensitive methods suitable for determination of different forms of bilirubin to various portable low cost systems applicable in point of care (POC) settings. In all these discussions emphasis is given on the novel methods and techniques bearing potential to measure the bilirubin level in biological samples reliably with less technical complexity and cost. We expect that this review will serve as a ready reference for the researchers and clinical professionals working on the subject and allied fields.

Operational impact of using a vanadate oxidase method for direct bilirubin measurements at an academic medical center clinical laboratory

Objectives

The aim of this study was to compare the operational impact of using vanadate oxidase versus diazo direct bilirubin assays for an academic medical center patient population.

Design and methods

Retrospective study was done over an approximately 3.5 year period. The main automated chemistry instrumentation was a Roche Diagnostics cobas 8000 line. The Roche Direct Bilirubin assay was compared to Diazyme Laboratories Direct Bilirubin Assay and Randox Laboratories Direct Bilirubin assay using manufacturer's guidelines for hemolysis index, lipemia index, and analytical measurement range (AMR).

Results

Retrospective data was analyzed for 47,333 serum/plasma specimens that had clinical orders for direct bilirubin. A total of 5943 specimens (12.6%) exceeded the hemolysis index limit for the Roche method compared to only 0.2% and 0.05% of specimens for the Diazyme and Randox methods, respectively. The impact was particularly large on patients less than 2 years old, for which 51.3% of specimens exceeded the hemolysis index for the Roche method. A total of 1671 specimens (3.5%) exceeded the lipemia index limit for the Roche method compared to less than 0.1% for the Randox method. Lastly, 988 (2.1%) of specimens had direct bilirubin concentrations exceeding the upper AMR limit of 10 mg/dL [171 µmol/L] for the Roche assay compared to less than 1% of specimens for the vanadate oxidase methods.

Conclusions

Vanadate oxidase direct bilirubin methods offer advantages over diazo methods in terms of less interference by hemolysis and lipemia, as well as wider AMR. The advantages are particularly evident for neonatal and infant populations.