In Vivo Monitoring of pH in Subacute PD Mouse Brains with a Ratiometric Electrochemical Microsensor Based on Poly(melamine) Films

Abstract

In vivo monitoring of cerebral pH is of great significance because its disturbance is related to some pathological processes such as neurodegenerative diseases, for example, Parkinson's disease (PD). In this study, we developed an electrochemical microsensor based on poly(melamine) (P Mel ) films for ratiometric monitoring of pH in subacute PD mouse brains. In this microsensor, P Mel films were prepared from a simple electropolymerization approach in a melamine-containing solution, serving as the selective pH recognition membrane undergoing a 2H + /2e − process. Meanwhile, electrochemically oxidized graphene oxide (EOGO) produced a built-in correction signal which helped avoid the environmental interference of the complicated brain systems. The potential difference between the peaks generated from EOGO and P Mel gradually decreased with the aqueous pH increasing from 4.0 to 9.0, constituting the detection foundation of the ratiometric electrochemical microsensor (REM). The in vitro studies demonstrated that this proposed method exhibited a high sensitivity (a Nernstian response of −61.35 mV/pH) and remarkable selectivity against amino acids, anions, cations, and biochemical and reactive oxygen species coexisting in the brain. Coupled with its excellent stability and reproducibility and good antibiofouling based on short-term detection, the developed REM could serve as a disposable sensor for the determination of cerebral pH in vivo. Its following successful application in the real-time measurement of pH in the striatum, hippocampus, and cortex of rat brains in the events of global cerebral ischemia/reperfusion verified the reliability of this method. Finally, we adopted this robust REM to systematically analyze and compare the average pH in different regions of normal and subacute PD mouse brains.

Efficient Electrochemical Microsensor for In Vivo Monitoring of H2O2 in PD Mouse Brain: Rational Design and Synthesis of Recognition Molecules

“…The PD mouse was set up and evaluated according to our previous report. ,, Then, a similar H 2 O 2 detection was carried out in different regions of the subacute PD mouse brain using the electrochemical microsensor designed by us, including the striatum, hippocampus, and cortex. As shown in Figure A–C, three peaks referring to the EOGO reference signal, AA, and H 2 O 2 levels were clearly observed on all of the detected DPV curves.…”

“…The graphene oxide (GO) suspension (1 mg/mL) was prepared well, and then CFME/GO electrode was prepared according to our previous reports. ,, The obtained CFME/GO electrode was subjected to potentiostatic electrochemical oxidation in 140 mM NaCl solution (parameters: voltage, 1.9 V; time, 200 s), thus producing a CFME/EOGO electrode. The procedure followed to construct the CFME/EOGO/Au/ o -Cl-DBP electrode on a CFME/EOGO electrode was the same as that used to construct a CFME/Au/ o -Cl-DBP electrode on a bare CFME electrode.…”

“…Animal experiments were based on our previous reports. ,, All experiments involving animals were conducted with the approval of the Animal Ethics Committee of the Hunan Normal University. For rats, male Sprague–Dawley rats (250–320 g) used for in vivo experiments were first anesthetized with chloral hydrate (25 mg/mL, an initial dose of 500 mg/kg (intraperitoneally)) with additional doses of 100 mg/kg (intraperitoneally) as required to maintain the anesthesia.…”

“…For mice, male C57BL mice (weighing 25–30 g) were used to set up the PD model mouse through i.p. injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) according to our previous reports. ,, Normal mice were injected with saline solution alone. The tip of the well-prepared electrochemical microsensor was inserted into different regions of the normal and PD mice, including the striatum (0.5 mm anterior to the bregma, 1.5 mm lateral to the midline, and 3.0 mm below the dura), the hippocampus (1.5 mm posterior to the bregma, 1.5 mm lateral to the midline, and 1.8 mm below the dura), and the cortex (2.0 mm posterior to the bregma, 0.25 mm lateral to the midline, and 1.2 mm below the dura).…”

“…Recently, designing recognition molecules and tailoring functional microsurfaces to fabricate robust electrochemical microsensors, converting chemical/electrochemical reactions into electric signals, have been verified to be efficient approaches with high sensitivity, selectivity, and accuracy to realize in vivo analysis of biomolecules such as pH, H 2 S, H n S n , l -cysteine, and various ions in the brain. ,− Inspired by this, we attempted to design specific recognition molecules for H 2 O 2 . As is well known, the specific reaction between boric acid esters and H 2 O 2 to produce phenol has been frequently used to design fluorescent probes. , In this regard, utilization of an electrochemically inactive boric acid ester to react with H 2 O 2 yielding phenol, thus generating an electrochemical signal, is expected to form the basis of the “off–on” switch mechanism for the electrochemical detection of H 2 O 2 .…”