Glass Electrode Research Articles

Fabrication and Optimization of Nafion as a Protective Membrane for TiN-Based pH Sensors.

In this study, a solid-state modified pH sensor with RF magnetron sputtering technology was developed. The sensor consists of an active electrode consisting of a titanium nitride (TiN) film with a protective membrane of Nafion and a reference glass electrode of Ag/AgCl. The sensitivity of the pH sensor was investigated. Results show a sensor with excellent characteristics: sensitivity of 58.6 mV/pH for pH values from 2 to 12, very short response time of approximately 12 s in neutral pH solutions, and stability of less than 0.9 mV in 10 min duration. Further improvement in the performance of the TiN sensor was studied by application of a Nafion protective membrane. Nafion improves the sensor sensitivity close to Nernstian by maintaining a linear response. This paves the way to implement TiN with Nafion protection to block any interference species during real time applications in biosensing and medical diagnostic pH sensors.

A novel miniaturized pH potentiometric electrode based on a nano bismuth oxide film deposited on a fluorine doped nano tin oxide glass substrate

A novel thin film of bismuth oxide (Bi2O3) deposited on a fluorine doped tin oxide glass substrate (FTO), using a spray pyrolysis technique, was prepared and used as a pH sensing membrane. The deposited Bi2O3 film was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). Film prepared by pyrolysis at 550 °C displayed a tetragonal β-phase of Bi2O3 with a porous structure, high roughness surface and nano cracks. The fabricated Bi2O3/FTO film was used as a miniaturized potentiometric electrode for monitoring a wide range of pH (pH 2 – 12) in aqueous solutions. The electrode exhibited an ideal near-Nernstian response (slope of −60.2 ± 0.3 mV/decade), high potential stability, mechanical durability and good selectivity toward some common interfering cations and anions, supporting its applicability for quality control/quality assurance purposes. The performance characteristics of the electrode and validation measurements, according to the standard methods, were evaluated. The Bi2O3/FTO-based electrode was satisfactorily used for monitoring the pH of some real water, beverages and fruit juice samples and the results compared fairly well with data obtained by the conventional pH glass electrode.

Biofunctionalized carbonaceous nanoflakes based efficient electrochemical biosensor for SAA biomarker detection

Swine flu is one of the major causes of death worldwide in both humans as well as in animals. In the biological sample of swine flu patients, there are several biomarkers secreted in which Serum Amyloid A (SAA) is one of the promising biomarker. Based on the concentration of SAA apolipoprotein, swine flu patients can be easily differentiated from the normal subject. Keeping these in view, we report the results of the studies related to the fabrication of an immunosensing platform for SAA apolipoprotein biomarker detection. For the fabrication of the immunosensing platform, we used ultrathin carbonaceous nanoflakes [Graphitic carbon nitride nanoflakes (g-C3N4NFs)] as transducer material. The g-C3N4NFs were prepared by polycondensation of melamine followed by liquid stripping, further treated with 3-(aminopropyl) triethoxysilane (APTES) to introduce amino group moiety. The APTES functionalized g-C3N4NFs were deposited onto ITO coated glass electrode using an electrophoretic deposition technique by providing an optimized DC potential of 30 V for 120 s. Further, biofunctionalization was done by immobilizing the specific anti-SAA monoclonal antibody onto APTES/g-C3N4NFs/ITO electrode via EDC-NHS chemistry and non-specific area were blocked with BSA molecules. Several non-distracting techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Fourier-transform infrared spectroscopy were used for the structural, morphological, and chemical characterization of synthesized nanomaterials as well as fabricated electrodes. Moreover, cyclic voltammetry techniques were used for electrochemical characterizations as well as response studies. The fabricated immunosensing platform i.e., BSA/anti-SAA/APTES/g-C3N4NFs/ITO is capable to detect SAA protein with linear detection range of 10–100 μg mL−1, limit of detection of 6.17 μg mL−1 and sensitivity of 2.42 μA mL μg−1cm−2.

Nafion Modified Titanium Nitride pH Sensor for Future Biomedical Applications.

pH sensors are increasingly being utilized in the biomedical field and have been implicated in health applications that aim to improve the monitoring and treatment of patients. In this work, a previously developed Titanium Nitride (TiN) solid-state pH sensor is further enhanced, with the potential to be used for pH regulation inside the human body and for other biomedical, industrial, and environmental applications. One of the main limitations of existing solid-state pH sensors is their reduced performance in high redox mediums. The potential shift E0 value of the previously developed TiN pH electrode in the presence of oxidizing or reducing agents is 30 mV. To minimize this redox shift, a Nafion-modified TiN electrode was developed, tested, and evaluated in various mediums. The Nafion-modified electrode has been shown to shift the E0 value by only 2 mV, providing increased accuracy in highly redox samples while maintaining acceptable reaction times. Overcoming the redox interference for pH measurement enables several advantages of the Nafion-modified TiN electrode over the standard pH glass electrode, implicating its use in medical diagnosis, real-time health monitoring, and further development of miniaturized smart sensors.

Fe-Doped Carbon Dots as NIR-II Fluorescence Probe for In Vivo Gastric Imaging and pH Detection.

Carbon dots (CDs) with excellent cytocompatibility, tunable optical properties, and simple synthesis routes are highly desirable for use in optical bioimaging. However, the majority of existing CDs are triggered by ultraviolet/blue light, presenting emissions in the visible/first near-infrared (NIR-I) regions, which do not allow deep tissue penetration. Emerging research into CDs with NIR-II emission in the red region has generated limited designs with poor quantum yield, restricting their in vivo imaging applications due to low penetration depth. Developing novel CDs with NIR-II emissions and high quantum yield has significant and far-reaching applications in bioimaging and photodynamic therapy. Here, it is developed for the first time Fe-doped CDs (Fe-CDs) exhibiting the excellent linear relationship between 900-1200nm fluorescence-emission and pH values, and high quantum yield (QY-1.27%), which can be used as effective probes for in vivo NIR-II bioimaging. These findings demonstrate reliable imaging accuracy in tissue as deep as 4 mm, reflecting real-time pH changes comparable to a standard pH electrode. As an important example application, the Fe-CDs probe can non-invasively monitor in vivo gastric pH changes during the digestion process in mice, illustrating its potential applications in aiding imaging-guided diagnosis of gastric diseases or therapeutic delivery.

Functional assay of light-induced ion-transport by rhodopsins.

Microbial rhodopsins are photoreceptive membrane proteins found from diverse microorganisms such as archaea, eubacteria, eukaryotes and viruses. Many microbial rhodopsins possess ion-transport activity by light, such as channels and pumps, and ion-transporting rhodopsins are important tools in optogenetics that control animal behavior by light. Historically, molecular mechanism of rhodopsins has been studied by spectroscopic methods for purified proteins. On the other hand, ion-transport function has to be studied by different methods. This chapter introduces two methods of functional assay of ion-transporting rhodopsins by light. One is a patch clamp method using mammalian cells, and another is an ion-transport assay using pH electrode and microbial cells. These functional assay provides fundamental data of ion-transporting rhodopsins, and thus contributes to evaluation for optogenetic tools.

The environmentally friendly approaches based on the heterojunction interface of the LaFeO3/Fe2O3@g-C3N4 composite for the disposable and laboratory sensing of triclosan.

Triclosan (TCS) is a polychlorinated phenoxy phenol (PCPPs) used as a disinfectant and a broad-spectrum antibacterial and antifungal agent in personal hygiene products. TCS easily forms diphenyl ethers and dioxins, which are persistent organic pollutants. This work used a double approach for the TSC sensing: a) screen-printed (SPE) electrochemical platform for on-site application, modified with lanthanum iron oxide and graphitic carbon nitride composite (LaFeO3/Fe2O3@g-C3N4/SPE); and b) carbon paste electrode (CPE), modified with the same material and used in laboratory conditions. Linear range from 0.1 μM to 10 μM, the limit of detection (LOD) of 29 nM and the limit of quantification (LOQ) of 91 nM were obtained for CP electrode in BRBS pH 8. SPE showed the best analytical parameters in BRBS at pH 3, with a linear range from 0.3 μM to 7 μM, LOD of 0.09 μM and LOQ of 0.28 μM. Furthermore, the influence of potential interferents was investigated and proven to be negligible. Determination of TSC was performed to estimate the environmental impact of this compound as well as the practical usefulness of the proposed sensor in the real sample analysis, confirmed with a HPLC analysis.

Electrochemical Pourbaix diagrams of monolayer MoSSe with different atomic ratios of chalcogens

MoSSe material is a very promising photoelectric material, and its application environment is aqueous solution. However, there is no research of the electrochemical stability of MoSSe materials in aqueous solution. In this work, the Pourbaix diagrams of monolayer MoSSe with different atomic ratios of molybdenum, sulfur and selenium are constructed based on density functional theory, and the thermodynamic stabilities and electrochemical corrosion behaviors under different pH values and electrode potentials are studied. The study of the pourbaix diagram of MoSSe shows that part of the corrosion-free region of MoSSe exists within the stable region of water in the Pourbaix diagram, indicating that the MoSSe can exist stably in the water environment. Compared with alkaline solutions, MoSSe has good corrosion resistance in acidic solution and neutral solution. The Pourbaix diagram of Mo<sub>4</sub>S<sub>2</sub>Se<sub>6</sub>, Mo<sub>4</sub>S<sub>6</sub>Se<sub>2</sub>, Mo<sub>4</sub>S<sub>7</sub>Se and Mo<sub>4</sub>SSe<sub>7</sub> show that in the case of high molar fraction of sulfur in monolayer MoSSe with different atomic ratios of molybdenum, sulfur and selenium, the conditions for the stable existence of materials in aqueous solution can have a larger range, and the corrosion resistance becomes better. In the case of high molar fractions of selenium in monolayer MoSSe with different atomic ratios of molybdenum, sulfur and selenium, the range of conditions for the stable existence of materials in aqueous solution becomes smaller, and the corrosion resistance becomes worse. In this work, the stabilities and corrosion behaviors of monolayer MoSSe with different atomic ratios of molybdenum, sulfur and selenium in aqueous solution are predicted, and the degradation behaviors of MoSSe materials are further explored, which can provide theoretical guidance for the application of MoSSe materials in the field of optoelectronics.

New glass cathode materials for Li-ion battery: Ni-Co doping in Li-B-O based glass

Lithium-borate-based glass co-doped with nickel and cobalt ions was successfully fabricated by a two-step melt quenching method. The relationship between Ni and Co contents in the glasses was investigated, with a focus on their electrochemical properties and battery performance. Cyclic voltammetry was used to pre-investigate the electrochemical properties of the glass electrodes. It was found that the specific capacitance of all conditions was above 100 F/g. This preliminary study showed that the glass is feasible to use as a Li-ion battery cathode. The Co-rich content sample (NC11) exhibited the highest specific capacity of 380 mAh/g in the first cycle test. However, the specific capacity was dramatically decreased in subsequent cycles due to Li-ion trapping in the glass structure. Additionally, the higher amount of Ni ions in the co-doping Ni/Co-LBO glass enhanced the retention properties. This suggests that Ni-rich content could improve the release of free Li-ions from the host glass structure.

Designing of a unique bioreceptor and fabrication of an efficient genosensing platform for neonatal sepsis detection.

We report the results of studies related to the fabrication of a nanostructured graphene oxide (GO)-based electrochemical genosensor for neonatal sepsis detection. Initially, we selected the fimA gene of E. coli for nenonatal sepsis detection and further designed a 20-mer long amine-terminated oligonucleotide. This designed oligonucleotide will work as a bioreceptor for the detection of the virulent fimA gene. An electrochemical genosensor was further developed where GO was used as an immobilization matrix. For the formation of a thin film of GO on an indium tin oxide (ITO)-coated glass electrode, an optimized DC potential of 10 V for 90 s was applied via an electrophoretic deposition unit. Thereafter, the designed oligonucleotides were immobilized through EDC-NHS chemistry. The nanomaterial and fabricated electrodes were characterized via X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and cyclic voltammetry techniques. The fabricated genosensor (BSA/pDNA/GO/ITO) has the ability to detect the target fimA gene with a linear detection range of 10-12 M to 10-6 M, a lower detection limit of 10-12 M and a sensitivity of 114.7 μA M-1 cm-2. We also investigated the biosensing ability of the developed genosensor in an artificial serum sample and the obtained electrochemical results were within the acceptable percentage relative standard deviation (% RSD), indicating that the fabricated genosensor can be used for the detection of neonatal sepsis by using a serum sample.

PH response and mechanical properties of Fe2O3–TeO2-based glass/stainless steel enamel electrodes for pH sensors

Glass pH sensors are unsuitable for in vivo biomedical, clinical, or food applications because of the brittleness of glass and the difficulty in measuring small volumes. Enamel structures such as glass/stainless steel are candidates for glass-based pH electrodes. In this study, new enamel electrodes for pH sensors using Fe2O3–TeO2-based glass/stainless steel were developed. The effect of NiO addition to Fe2O3–TeO2 glass on the pH sensitivity and the three-point bending strength of enamels were investigated. The effect of NiO addition to Fe2O3–TeO2 glass/stainless steel on the pH sensitivity was negligible. Fe2O3–TeO2-based glass/stainless steel showed pH sensitivity appropriate to a working electrode. Enameling at a lower temperature under an air atmosphere was desirable for narrowing the gap between pH 4–7 and pH 7–9 sensitivities. The NiO addition to Fe2O3–TeO2 glass/stainless steel decreased the three-point bending strength. Therefore, NiO did not serve as an adhesion oxide in the Fe2O3–TeO2 glass. Fe2O3–TeO2 glass/stainless steel possessed the highest three-point bending strength among all samples when prepared at 670 °C under an air atmosphere. Therefore, no NiO addition and enameling at a lower temperature under an air atmosphere are desirable for obtaining more robust Fe2O3–TeO2 glass/stainless steel than Li2O–SiO2-based glass electrodes for pH sensors.

Effect of Ni-Co transition metal ratios on structure-function of Lithium Aluminium Borate Glasses for battery electrode

The Lithium Aluminum Borate Glasses (Li2O-Al2O3-B2O3) doped with various concentrations of xNi: Co (where x = 1, 2, 3, and 4) effectively synthesized by melt-quench process. Glasses made of nickel-lithium borate have undergone rigorous study to determine the impact of nickel-cobalt content on the operation of electrochemical characteristics and battery performance. The phase structure of all samples was confirmed using TEM diffraction XRD patterns. Intriguingly, at a scan rate of 5 mV/s, the 1Ni: Co glass electrode displayed the highest specific capacitance of 76.6 F/g. By adjusting the Ni:Co ratio in the glass structure, produced (Li2O-Al2O3-B2O3) glasses exhibit improved electrochemical characteristics.

Insight into the role of nitrogen in N-doped ordered mesoporous carbons for the spontaneous non-covalent attachment and electrografting of redox-active materials.

The role of nitrogen functional groups in nitrogen-doped ordered mesoporous carbons (OMCs) toward the spontaneous non-covalent and electrografting was investigated using two home-made ionic liquid-derived ordered mesoporous carbons having different nitrogen concentrations (guanine-rich ionic liquid-derived ordered mesoporous carbon (GIOMC) and ionic liquid-derived ordered mesoporous carbon (IOMC)). The carbonaceous materials were fabricated by the carbonization of a mixture of ionic liquid (1-methyl-3-phenethyl-1H-imidazolium hydrogen sulfate) as a carbon source using SBA-15 as a hard template. Guanine was used during the carbonization of GIOMC as a nitrogen source. The electrode was modified with either GIOMC or IOMC followed by electrochemical surface functionalization with a few electro-active precursors as redox-active molecular models bearing different substituents and electronic properties. The high surface coverage of 5.6(±0.3) × 10-9 mol cm-2 for 4,4-biphenol was obtained for the GIOMC-modified electrode. We seek to explain whether the nitrogen content could indeed exert a dramatic impact on loading electroactive species on the electrode surface. The non-covalent anchoring studies indicated that at higher pH values the loading of electro-active moieties was significantly influenced by the content of nitrogen on the employed OMCs. The adsorption capacity (mg g-1) of the OMCs was studied for catechol as a typical electro-active species in the range of 0.050-0.165 mg ml-1. The adsorption capacity of 0.11 mg g-1 catechol was 42(±4) and 26(±3) mg g-1 for GIOMC and IOMC, respectively. In addition, our observations revealed that electro-grafting efficiency via diazonium ion was restricted by the protonation of nitrogen in the reaction media. Further, the fabricated redox-active/N-doped OMC electrodes showed sensitivity to pH, which was accompanied by either a Nernstian shift of the redox peak potentials (60(±3) mV per pH) in the pH range of 2-13 in the buffer solutions or variations of the redox peak currents (9.7(±0.3) μA per pH) in the pH range of 1-5.5 in the unbuffered situations. The resulting electrodes as voltammetric pH probes showed a simple response to pH in both buffer and unbuffered solutions. In addition, we introduced the fabricated electrode as a zero-gap generator/collector electrode system using a single electrode to recognize proton-dependent electron transfer from the proton-independent electrode process by detecting pH changes quite close to the surface of the electrode. The detailed descriptions are outlined.

Electrochemical Synthesis of Polycarbazole Film in Nonacidic Medium and its Electrochromic Properties

This study is about the electrochemical polymerization of the monomer of carbazole, whose anodic polymerization is very common in the literature. When the studies in the literature were examined, it was seen that the electrochromic properties of carbazole were not examined. For this purpose, electrochemical and optical properties were investigated in detail by polymerizing carbazole on both glassy carbon and ITO glass electrodes in 0.1 M TABPF6/ DCM medium using the cyclic voltammetry method. The polymer film synthesized by electroanalytical methods showed reversible electrochemical oxidation process properties as well as electrochromic properties. The polymer film synthesized by electroanalytical methods showed reversible electrochemical oxidation process properties as well as electrochromic properties. Considering that this study will form a basis for other studies, it is thought that the evaluation of carbazole monomer in terms of its electrochromic properties will provide a great deal to the literature.

Mesoporous perovskite-type La0.8Sr0.2Cu0.7Mn0.3O3/SiO2 nanocomposite-decorated-graphene-oxide nanosheets: Green synthesis and application in the sensitive determination of Morin in kiwi fruit samples

Perovskite nanocrystals (PNCs) are highly tolerant to defects, unlike metal chalcogenides, and do not need surface passivation to retain high quantum yields. Remarkably, the defect structures and trap states in perovskites are often found only in their conduction and/or valence bands and not in the mid-states of the bandgap. Such intrinsic features of them essentially boost their properties and largely favor their sensing applications. In the present research work, perovskite/graphene oxide nanosheets were used to modify the surface of a glassy carbon electrode to the determination of the Morin in the kiwifruit samples. For this purpose, perovskite nanosheets were synthesized using the sol-gel method and combined with graphene oxide, which was prepared using Hummer’s method, to prepare the modifier suspension. To ensure the effective synthesis of the perovskite nanosheets, the morphological study has been applied and the modified electrode was examined by various characterization techniques. The electrochemical behavior of Morin on the surface of the modified carbon glass electrode was investigated using the cyclic voltammetry (CV) technique. The analytical figure of merits including the linear range of 10–110 μM and a detection limit of 4.49 μM were obtained. Finally, the designed sensing assay was efficiently applied for the determination of Morin in kiwifruit. The results obtained from the prepared sensor indicate suitable analytical properties including low detection limits, wide linear range, and good performance for the determination of Morin. Moreover, to check the accuracy of the proposed assay, the recovery index of 97 % indicates high performance in real samples. Stability, repeatability, and high reproducibility of the modified electrode are other prominent analytical features of the designed sensor. Consequently, it was possible to verify that the sensing assay has the potential for being desirably utilized in the determination of Morin in various real samples.

An ultrasensitive electrochemical DNA biosensor for monitoring Human papillomavirus-16 (HPV-16) using graphene oxide/Ag/Au nano-biohybrids

A DNA-based electrochemical biosensor has been developed herein for the detection of Human papillomavirus-16 (HPV-16). HPV-16 is a double-stranded, non-enveloped, epitheliotropic DNA virus which responsible for cervical cancer. In this proposed biosensor, an indium tin oxide (ITO) coated glass electrode was modified for sensing HPV-16 using graphene oxide and silver coated gold nanoparticles. Subsequently, HPV-16 specific DNA probes were immobilized on a modified ITO surface. The synthesized nanocomposites were characterized by FE-SEM and UV-VIS spectroscopy techniques. Electrochemical characterization was performed by using cyclic voltammetry and electrochemical Impedance Spectroscopy methods. The hybridization between the probe and target DNA was analyzed by a reduction in current, mediated by methylene blue. The biosensor showed a qualitative inequity between the probe and target HPV-16 DNA. The developed biosensor showed high sensitivity as 0.54 mA/aM for the detection of HPV-16. In a linear range of 100 aM to 1 μM with 100 aM LOD, the proposed biosensor exhibited excellent performance with the rapid diagnosis. Thus, the results indicate that the developed HPV DNA biosensor shows good consistency with the present approaches and opens new opportunities for developing point-of-care devices. The diagnosis of HPV-16 infection in its early stage may also be possible with this detection system.

Potentiometrie and spectroscopic study of isoniazid - an anti-tubercular drug

The copper, nickel and zinc complexes of isoniazid (ISO, isonicotinic acid hydrazide), an anti-tubercular drug, have been investigated to determine whether these metal-ions improve the permeability and bioavailability of the drug. Since such properties of isonazid depend on its solution speciation, the latter was investigated by determining the equilibrium constants for the reaction of H+, Cu(II), Ni(II) and Zn(II) with isonazid in aqueous solution at 25.00 ± 0.01 °C and 0.15 M (NaCl), using glass electrode potentiometry. The structure of the copper complex of isoniazid was investigated using ultraviolet-visible spectroscopy. The results support the structures postulated from the potentiometric data. This study also considered membrane permeability using a Franz cell and octanol/water distribution coefficients. Distribution coefficient studies showed that ISO and its metal complexes are hydrophilic. The incorporation of a metal-ion improves the hydrophilicity of the ligand. The presence of a metal ion greatly enhanced the permeation of ISO through an artificial membrane in the order Cu(II) > Ni(II) > Zn(II) > ISO at pH 2 and Zn(II) > Ni(II) > ISO > Cu(II) at pH 4.

Symmetric cell for improving solid-contact pH electrodes

Traditional pH glass electrodes are designed in a symmetrical manner to guarantee the most reliable and reproducible potentiometric measurements possible. Solid-contact and other pH probes not based on glass membranes are desirable because they allow for new types of applications, may be mass fabricated and less prone to breakage. Unfortunately, however, they introduce electrochemical asymmetry because the reference element used in the reference electrode compartment is now different. This work shows how symmetry may be restored with solid-contact pH probes, using a H+-selective ionophore-based polymeric membrane deposited on top of a conductive polymer (PEDOT-C14) as a transducer layer. The new cell implements a reference element that is composed of a similarly formulated pH probe immersed into a buffer solution and an Ag/AgCl element directly connected to a single-junction Ag/AgCl/3.0 M KCl reference electrode that is placed in contact with the sample solution. By implementing this design, the zero point of the solid-contact pH sensing system may be shifted to the conventional value of pH 7.0. The value of the zero point was experimentally confirmed as 6.96 ± 0.02 pH units at three different temperatures in the range from 5 to 25 °C. This symmetric solid-contact potentiometric cell gave a long-term potential drift of 48 ± 16 μV h−1, comparable to that of a combination pH glass electrode.

Assessment of Heavy Metals Content in Soil and Groundwater within the Vicinity of Automobile Mechanic Workshops in Yola and Jimeta Towns, Adamawa State, Nigeria

Although heavy metals are naturally occurring elements that are found throughout the earth’s crust, anthropogenic activities such as mechanic workshops are a source of concern for heavy metal contamination. This paper assessed the heavy metals content in soil and groundwater within the vicinity of automobile mechanic workshops in Yola and Jjimeta Towns, Adamawa State, Nigeria using standard methods. Heavy metals were determined using AAS model 210 VGP while pH was determined by electronic JENWAY glass electrode pH meter (Model 3510). Data obtained revealed that, the pH of the sample ranged from 7.52 to 5.19 (provide the average pH levels in the soil and groundwater). From the study conducted, (provide the mean of the heavy metals here) it can be seen that the level of heavy metals found in the soil is in the order of Zn>Ni>Fe>Pb>Cd. While heavy metals found in the ground water of automobile mechanic locations is in the order Ni>Fe>Zn>Cd>Pb. The levels of metals found in the present study were generally below the Department of Petroleum of Petroleum Resources target values for metals in soils.

Non-destructive Approach for the Prediction of pH in Frozen Fish Meat Using Fluorescence Fingerprints in Tandem with Chemometrics

The pH of fish muscle is an important index for quality assessment, but the traditional methods using a pH meter and probe/electrode are destructive, time-consuming, and laborious, making them unsuitable for on-line meat-quality monitoring. Hence, an approach of using fluorescence fingerprints (FFs) for the non-destructive prediction of pH in frozen fish fillets was trialled. Sixty-three live horse mackerel (Trachurus japonicus) and spotted mackerel (Scomber australasicus) were freshly harvested, sacrificed instantly, then preserved in ice, filleted, vacuum-packed, and frozen. Subsequently, the FFs of all frozen fillets were recorded using a fibreoptic-equipped fluorescence spectrometer, and the corresponding pH values of the samples were measured. After pre-processing, the masked FFs were modelled using partial least squares regression (PLSR) for the prediction of pH values. The results revealed that the developed method was accurate enough for predicting the pH changes in frozen horse mackerel and spotted mackerel fillets with R2 = 0.71 and R2 = 0.90, respectively. The proposed technique could be utilized as a rapid and non-contact alternative to traditional pH electrodes for the quality monitoring of fish products.