Potassium ferrocyanide k4fe cn 6 3h2o

Kappa-carrageenan is a natural polysaccharide extracted from red algae of the genus Halurus (MW = 750 kDa) with a polydispersity index of 1.7. Chitosan (average MW = 45 kDa with a degree of acetylation >75%) was obtained from Sigma-Aldrich. Citrate gold nanoparticles (AuNPs, 23 nm) were synthesized using the classic citrate reduction method [21 (link)]. Glutaraldehyde (GA, 25 wt% aqueous solution), 4-aminothiolphenol (4-ATP, 97%), and the enzyme glucose oxidase extracted from Aspergillus niger (GOD, 100–250 kU/g solid, type X-S) were purchased from Sigma-Aldrich (Saint-Quentin-Fallavier, France). N-(2-Hydroxyethyl) piperazine-N′-(2-ethanesulfonic acid) (HEPES), acetic acid (99.8%), and D-(+)-Glucose were also purchased from Sigma-Aldrich. The ethanol, acetone, sulfuric acid (95%), and hydrogen peroxide (30% in water) were purchased from Fluka and used for gold electrode pretreatment. Phosphate buffered saline (PBS, pH 7.4, 0.1 M) was prepared from monopotassic and dipotassic phosphate salts, sodium and potassium chlorides from Sigma-Aldrich and adjusted to pH 7.4. Potassium ferricyanide [K₃Fe(CN)₆] and potassium ferrocyanide [K₄Fe(CN)₆·3H₂O] were provided by Sigma-Aldrich. All reagents were used without further purification. Aqueous solutions were prepared using ultrapure water from a MilliQ purification system.

Ficus sycomorus leaves were sourced from Al-Shohdaa city, Menoufia governorate, Egypt. No permissions were required prior to collecting the plant leaves. The Botany Department of the Menoufia University, Egypt, recognized them. Silver nitrate as the AgNP precursor was obtained from Cambrian Chemicals. BG, methyl orange, phenolphthalein, eriochrome black T dyes and potassium ferrocyanide (k₄[Fe(CN)₆].3H₂O) were obtained from Sigma-Aldrich. The components of acetate buffer solution, acetic acid and sodium acetate (CH₃COONa.3H₂O) were bought from Sigma-Aldrich.

L-glutamate oxidase (GluOx) from Streptomyces sp., L-glutamic acid (99%), Nafion^® perfluorinated resin solution (Nafion, 5 wt.%), gold (III) chloride trihydrate (HAuCl₄⋅3H₂O, 99.9%), ascorbic acid (AA, 99.7%), dopamine (DA, 98%), uric acid (UA, 99%), sodium sulfate anhydrous (Na₂SO₄, 99%), sulfuric acid (H₂SO₄, 99.99%), potassium chloride (KCl, 96%), phosphate buffer saline (PBS, pH = 7.2), potassium ferricyanide (K₃[Fe(CN)₆]), and potassium ferrocyanide (K₄Fe(CN)₆·3H₂O) were all purchased from Sigma-Aldrich. Monolayer graphene oxide aqueous dispersion (GO, 10 mg/g) was obtained from C6G6 Technology Co., Ltd. (Hangzhou, China). Artificial cerebrospinal fluid (ACSF) was purchased from Beijing Leagene Biotechnology Co., Ltd. (Beijing, China). All solutions were stored at 4 °C and protected from light. Unless otherwise stated, all chemicals were used as received.

Chemicals like dopamine
(98%), agar (99%), glutaraldehyde (GA) (50% in H₂O), d-glucose (99.5%), methylene bis(acrylamide) (MBA) (99%), uric
acid (≥99%), ethanol (≥99.8%), potassium chloride (KCl)
(≥99%), glycerol (≥99%), acetone (≥99.9%), sodium
hydrogen phosphate (Na₂HPO₄) (≥99%),
calcium chloride (CaCl₂) (≥97%), magnesium dichloride
(MgCl₂) (≥98%), ascorbic acid (99%), sodium chloride
(NaCl) (≥99%), potassium hydrogen phosphate (K₂HPO₄) (98%), and potassium ferrocyanide (K₄[Fe(CN)₆]·3H₂O) (≥98.5%) were used for the
sensor designed and were supplied from Sigma-Aldrich. 0.9% isotonic
sodium chloride solution was purchased from the local pharmacy. A
potentiostat device (triple electrode system) that was used for measurements
was purchased from CH Instruments. Deionized (DI) water that was used
for measurements was obtained from a Milli-Q water purification system.
All glassy materials were washed with DI water, ethanol, and acetone.