Determination of three Tumor Biomarkers (Homovanillic Acid, Vanillylmandelic Acid, and 5-Hydroxyindole-3-Acetic Acid) Using Flow Injection Analysis with Amperometric Detection

Preparation of gold nanoparticles loaded MOF-199 for SERS detection of 5-hydroxyindole-3-acetic acid in serum

5-Hydroxyindole-3-acetic acid (5-HIAA) is regarded as a biomarker for diagnosis of carcinoid tumors, and it is of great significance to developing a precision assay for monitoring 5-HIAA levels. In this work, gold nanoparticles loading on the surface of MOF-199 (Au NPs/MOF-199) is prepared to propose a surface enhanced Raman scattering (SERS) assay for 5-HIAA. When 4-mercaptopyridine (4-MPy) is used as a SERS probe, on Au NPs/MOF-199, limit of detection (LOD) at 10-9 mol/L can be achieved. In addition, Au NPs/MOF-199 substrate with good preparation reproducibility shows long-term storage stability at 4 °C. Under optimal condition, the Au NPs/MOF-199-based SERS method is applied to determine 5-HIAA in serum. The concentration linear range is from 10-9 to 10-5 mol/L and LOD is of 6.40 × 10-11 mol/L. Much importantly, Au NPs/MOF-199 substrate exhibits specific response toward 5-HIAA against other metabolites in the serum due to the capturing selectivity from porous MOF-199. The recoveries obtained on spiked human serum samples locate in the span from 94.30% to 106.00% with RSD of 4.01-7.43%. Au NPs/MOF-199-based SERS sensing strategy is a promising avenue for on-field monitoring biomedical species for clinic diagnosis purpose.

Novel Lanthanide-Based Metal-Organic Framework Isomer as a Double Ratiometric Fluorescent Probe for Vanillymandelic Acid

The concentration of vanillymandelic acid (VMA) in urine is closely related with pheochromocytoma diagnosis. Thus, it is essential to develop more accurate and convenient fluorescence sensing strategies toward VMA. Until now, the design of double ratiometric detection methods for VMA was still in the unexplored stage. In this work, novel Ln³⁺-based metal-organic frameworks (QBA-Eu and QBA-Gd_0.875Eu_0.125) possessing dual emission peaks was fabricated successfully, which served as isomers of YNU-1 and exhibited more excellent water stability in fluorescence and structure than the ones of YNU-1. The formation of the complex between QBA ligands and VMA molecules via hydrogen bonds within QBA-Eu frameworks produced a new emission band centered at 450 nm and resulted in the decline of monomer emission intensity for QBA at 390 nm. Owing to the reduced energy gap [ΔE (S₁ - T₁)], the antenna effect was hampered and luminescence of Eu³⁺ ions also decreased. The developed double ratiometric (I_615nm/I_475nm, I_390nm/I_475nm) fluorescence sensors based on QBA-Eu and QBA-Gd_0.875Eu_0.125 possessed the advantages of fast response (4 min), low detection limits (0.58 and 0.51; 0.22 and 0.31 μM), and wide linear ranges (2-100 and 2-80 μM), which met the requirements of pheochromocytoma diagnosis. We also applied them to determine VMA in an artificial urine sample and diluted human urine sample and obtained satisfactory results. They will become prospective fluorescence sensing platforms for VMA.

Stable Lanthanide-Organic Frameworks: Crystal Structure, Photoluminescence, and Chemical Sensing of Vanillylmandelic Acid as a Biomarker of Pheochromocytoma

Several isostructural lanthanide metal-organic frameworks, viz. [Ln(DCHB)_1.5phen]_n (Ln-MOFs, where Ln = Eu for 1, Tb for 2, Sm for 3 and Dy for 4), are successfully synthesized through the hydrothermal reactions of 4'-di(4-carboxylphenoxy)hydroxyl-2, 2'-bipyridyl (H₂DCHB) and lanthanide nitrates as well as chelator 1,10-phenantroline (phen). These structures are characterized by single-crystal X-ray diffraction, and the representative Ln-MOF 1 is a fivefold interpenetrated framework with the uncoordinated Lewis base N sites form DCHB^2- ligands. The photoluminescence research studies reveal that Ln-MOFs 1-4 exhibit characteristic fluorescent emissions from ligand-induced lanthanide Ln(III) ions, while the single-component emission spectra of Ln-MOF 4 are all located in a white region under different excitations. The absence of coordinated water and the interpenetration property of the structures are conducive to the structure rigidity, and the results display that Ln-MOF 1 has high thermal/chemical stabilities in common solvents and a wide pH range as well as the boiling water. Notably, luminescent sensing studies reveal that Ln-MOF 1 with prominent fluorescence properties can perform in highly sensitive and selective sensing of vanillylmandelic acid (VMA) in aqueous systems (K_SV = 562.8 L·mol^-1; LOD = 4.6 × 10^-4 M), which can potentially establish a detection platform for the diagnosis of pheochromocytoma via multiquenching mechanisms. Moreover, the 1@MMMs sensing membranes comprised of Ln-MOF 1 and a poly(vinylidene fluoride) (PVDF) polymer can also be facilely developed for VMA detection in aqueous media, suggesting the enhanced convenience and efficiency of practical sensing applications.

A light-operated dual-mode method for neuroblastoma diagnosis based on a Tb-MOF: from biometabolite detection to logic devices

Tb-DBA can not only serve as a light-operated dual-mechanism driven platform to detect VMA (an early pathological feature of neuroblastoma), but can also produce a different fluorescence response to epinephrine (EP, the metabolic precursor of VMA).

Screen-Printed Technologies Combined with Flow Analysis Techniques: Moving from Benchtop to Everywhere

Screen-printed electrodes (SPEs) coupled with flow systems have been reported in recent decades for an ever-growing number of applications in modern electroanalysis, aiming for portable methodologies. The information acquired through this combination can be attractive for future users with basic knowledge, especially due to the increased measurement throughput, reduction in reagent consumption and minimal waste generation. The trends and possibilities of this set rely on the synergistic behavior that maximizes both SPE and flow analyses characteristics, allowing mass production and automation. This overview addresses an in-depth update about the scope of samples, target analytes, and analytical throughput (injections per hour, limits of detection, linear range, etc.) obtained by coupling injection techniques (FIA, SIA, and BIA) with SPE-based electrochemical detection.

Electrochemical sensor based on MIP for highly sensitive detection of 5-hydroxyindole-3-acetic acid carcinoid cancer biomarker in human biological fluids

An electrochemically synthetized nano-sensor based on molecularly imprinted polypyrrole (MIPPy) was successfully developed for the detection of 5-hydroxyindole-3-acetic acid (5-HIAA) in human biological fluids namely serum, urine, and plasma. The imprinted glassy carbon electrode was prepared by electropolymerisation of pyrrole via cyclic voltammetry (C.V). After completely leaching the imprinted molecules from the polymeric network, complementary cavities are created. The developed MIPPy sensor, under optimized conditions, shows a high sensitivity towards the target molecule (LOQ = 5 × 10^-11 M). Moreover, it presents a wide linear response in the range of 5 × 10^-11 - 5 × 10^-5 M (R² > 0.999) with a detection limit of 15 × 10^-12 M. In order to evaluate the selectivity of the MIPPy film, several structural analogues and compounds forming the real matrices were tested. The obtained results show an excellent recovery rate (between 98.86 and 101.52%) proving the promising application of the proposed nano-sensor in the detection of 5-HIAA in human biological fluids without any significant interference recorded.

Differential pulse voltammetric determination of homovanillic acid as a tumor biomarker in human urine after hollow fiber-based liquid-phase microextraction

Novel method for the determination of a tumor marker homovanillic acid (HVA) in human urine was developed. Combination of hollow fiber - based liquid-phase microextraction (HF-LPME) and differential pulse voltammetry (DPV) at a cathodically pre-treated boron doped diamond electrode (BDDE) was applied for these purposes. Optimum conditions were: butyl benzoate as supported liquid membrane (SLM) formed on polypropylene HF, 0.1 mol L^-1 HCl as donor phase, 0.1 mol L^-1 sodium phosphate buffer of pH 6 as acceptor phase, and 30 min extraction time. HF-LPME-DPV concentration dependence was linear in the range from 1.2 to 100 μmol L^-1. Limits of quantification (LOQ) and detection (LOD) were 1.2 and 0.4 μmol L^-1, respectively. The applicability of the developed method was verified by analysis of human urine. Standard addition method was used, found HVA concentration was 13.5 ± 1.3 μmol L^-1, RSD = 9.3% (n=5).

Structure Engineering of a Lanthanide-Based Metal-Organic Framework for the Regulation of Dynamic Ranges and Sensitivities for Pheochromocytoma Diagnosis

Exploring innovative technologies to precisely quantify biomolecules is crucial but remains a great challenge for disease diagnosis. Unfortunately, the humoral concentrations of most biotargets generally vary within rather limited scopes between normal and pathological states, while most literature-reported biosensors can detect large spans of targets concentrations, but are less sensitive to small concentration changes, which consequently make them mostly unsatisfactory or even unreliable in distinguishing positives from negatives. Herein, a novel strategy of precisely quantifying the small concentration changes of a certain biotarget by editing the dynamic ranges and sensitivities of a lanthanide-based metal-organic framework (Eu-ZnMOF) biosensor is reported. By elaborately tailoring the biosensor's structure and surface areas, the tunable Eu-ZnMOF is developed with remarkably enhanced response slope within the "optimized useful detection window," enabling it to serve as a powerful signal amplifier (87.2-fold increase) for discriminating the small concentration variation of urinary vanillylmandelic acid (an early pathological signature of pheochromocytoma) within only three times between healthy and diseased subjects. This study provides a facile approach to edit the biosensors' performances through structure engineering, and exhibits promising perspectives for future clinical application in the non-invasive and accurate diagnosis of severe diseases.

Strain engineered biocompatible h-WO3 nanofibers based highly selective and sensitive chemiresistive platform for detection of Catechol in blood sample

In this work, we demonstrate a simple, low-cost biocompatible 1D-WO₃ electrospun nanofibers based strain-induced high-performance chemiresistive catechol sensor. WO₃ nanofibers were synthesized using e-spinning, annealed and drop-casted on to flexible PET substrate. X-Ray Diffraction (XRD) studies confirm the formation of Hexagonal phase-WO₃ and Raman spectroscopy proved the presence of O-W-O bending modes. Field emission scanning electron microscopy (FESEM) images displayed the random orientation of dense WO₃ nanofibers on PET substrate. Hall measurements confirmed the formation of n-type WO₃ nanofibers with carrier density of 10¹⁹ cm^-3. The sensor responded to a broad dynamic range of catechol concentrations from 1 μM to 100 μM with sensitivity of 51.29 μM^-1 cm^-2 and limit of detection of 0.52 μM which are better than previously reported catechol sensors. Interestingly, upon application of compressive strain to the flexible sensor, a remarkable increase in sensitivity to 88.34 μM^-1 cm^-2 was observed with further reduction of the limit of detection to 42 nM. Upon subjecting the sensor to strain ranging from 3.14% to 47.6%, an increase in sensitivity to catechol was observed due to the increase in the exposed surface area of interconnected WO₃ nanofibers which enhances the active sites for catechol oxidation by enhancing the tunneling current. The sensor could detect catechol in simulated blood samples with excellent selectivity against AA, UA, Na⁺, Ca⁺, hydroquinone and glucose.