70 research outputs found
Designing Recognition Molecules and Tailoring Functional Surfaces for In Vivo Monitoring of Small Molecules in the Brain
ConspectusThe in vivo analysis of chemical signals in brain extracellular
fluid (ECF) using implanted electrochemical biosensors is a vital
way to study brain functions and brain activity mapping. This approach
offers excellent spatial (10–200 μm) and temporal (approximately
second) resolution and the major advantage of long-term stability.
By implantation of a microelectrode in a specific brain region, changes
in the concentration of a variety of ECF chemical species can be monitored
through applying a suitable electrical signal and, typically, recording
the resulting Faradaic current. However, the high performance requirements
for in vivo biosensors greatly limit our understanding of the roles
that biomolecules play in the brain. Since a large number of biological
species, including reactive oxygen species (ROS), metal ions, amino
acids, and proteins, coexist in the brain and interact with each other,
developing in vivo biosensors with high selectivity is a great challenge.
Meanwhile, it is difficult to quantitatively determine target molecules
in the brain because of the variation in the distinct environments
for monitoring biomolecules in vitro and in vivo. Thus, there are
large errors in the quantification of concentrations in the brain
using calibration curves obtained in artificial cerebrospinal fluid
(aCSF). More importantly, to gain a full understanding of the physiological
and pathological processes in the brain, the development of novel
approaches for the simultaneous determination of multiple species
in vivo is urgently needed.This Account provides insight into
the basic design principles
and criteria required to convert chemical/electrochemical reactions
into electric signals, while satisfying the increasing requirements,
including high selectivity, sensitivity, and accuracy, for the in
vivo analysis of biomolecules in the brain. Recent developments in
designing various functional surfaces, such as self-assembled monolayers,
gold nanostructures, and nanostructured semiconductors for facilitating
electron transfer from specific enzymes, including superoxide dismutase
(SOD), and further application to an O<sub>2</sub><sup>•–</sup> biosensor are summarized. This Account also aims to highlight the
design principles for the selective biosensing of Cu<sup>2+</sup> and
pH in the brain through the rational design and synthesis of specific
recognition molecules. Additionally, electrochemical ratiometric biosensors
with current signal output have been constructed to correct the effect
of distinct environments in a timely manner, thus greatly improving
the accuracy of the determination of Cu<sup>2+</sup> in the live brain.
This method of using a built-in element has been extended to biosensors
with the potential signal output for in vivo pH analysis. More importantly,
the new concept of both current and potential signal outputs provides
an avenue to simultaneously determine dual species in the brain.The extension of the design principles and developed strategy demonstrated
in this Account to other biomolecules, which may be closely correlated
to the biological processes of brain events, is promising. The final
section of this Account outlines potential future directions in tailoring
functional surfaces and designing recognition molecules based on recent
advances in molecular science, nanoscience and nanotechnology, and
biological chemistry for the design of advanced devices with multiple
target species to map the molecular imaging of the brain. There are
still opportunities to engineer surfaces that improve on this approach
by constructing implantable, multifunctional nanodevices that promise
to combine the benefits of multiple sensing and therapeutic modules
Micro Electrochemical pH Sensor Applicable for Real-Time Ratiometric Monitoring of pH Values in Rat Brains
To
develop in vivo monitoring meter for pH measurements is still
the bottleneck for understanding the role of pH plays in the brain
diseases. In this work, a selective and sensitive electrochemical
pH meter was developed for real-time ratiometric monitoring of pH
in different regions of rat brains upon ischemia. First, 1,2-naphthoquinone
(1,2-NQ) was employed and optimized as a selective pH recognition
element to establish a 2H<sup>+</sup>/2e<sup>–</sup> approach
over a wide range of pH from 5.8 to 8.0. The pH meter demonstrated
remarkable selectivity toward pH detection against metal ions, amino
acids, reactive oxygen species, and other biological species in the
brain. Meanwhile, an inner reference, 6-(ferrocenyl)Âhexanethiol (FcHT),
was selected as a built-in correction to avoid the environmental effect
through coimmobilization with 1,2-NQ. In addition, three-dimensional
gold nanoleaves were electrodeposited onto the electrode surface to
amplify the signal by ∼4.0-fold and the measurement was achieved
down to 0.07 pH. Finally, combined with the microelectrode technique,
the microelectrochemical pH meter was directly implanted into brain
regions including the striatum, hippocampus, and cortex and successfully
applied in real-time monitoring of pH values in these regions of brain
followed by global cerebral ischemia. The results demonstrated that
pH values were estimated to 7.21 ± 0.05, 7.13 ± 0.09, and
7.27 ± 0.06 in the striatum, hippocampus, and cortex in the rat
brains, respectively, in normal conditions. However, pH decreased
to 6.75 ± 0.07 and 6.52 ± 0.03 in the striatum and hippocampus,
upon global cerebral ischemia, while a negligible pH change was obtained
in the cortex
Mitochondria-Targeted Ratiometric Fluorescent Nanosensor for Simultaneous Biosensing and Imaging of O<sub>2</sub><sup>•–</sup> and pH in Live Cells
Intracellular
pH undertakes critical functions in the formation
of a proton gradient and electrochemical potential that drives the
adenosine triphosphate synthesis. It is also involved in various metabolic
processes occurring in mitochondria, such as the generation of reactive
oxygen species, calcium regulation, as well as the triggering of cell
proliferation and apoptosis. Meanwhile, the aberrant accumulation
of O<sub>2</sub><sup>•–</sup> within mitochondria is
frequently intertwined with mitochondrial dysfunction and disease
development. To disentangle the complicated inter-relationship between
pH and O<sub>2</sub><sup>•–</sup> in the signal transduction
and homeostasis in mitochondria, herein we developed a mitochondria-targeted
single fluorescent probe for simultaneous sensing and imaging of pH
and O<sub>2</sub><sup>•–</sup> in mitochondria. CdSe/ZnS
quantum dots encapsulated in silica shell was designed as an inner
reference element for providing a built-in correction, as well as
employed as a carrier to assemble the responsive elements for O<sub>2</sub><sup>•–</sup> and pH, together with mitochondria-targeted
molecule. The developed nanosensor demonstrated high accuracy and
selectivity for pH and O<sub>2</sub><sup>•–</sup> sensing,
against other ROS, metal ions, and amino acids. The remarkable analytical
performance of the present nanosensor, as well as good biocompatibility,
established an accurate and selective approach for real-time imaging
and biosensing of O<sub>2</sub><sup>•–</sup> and pH
in mitochondria of live cells
Ratiometric Electrochemical Sensor for Selective Monitoring of Cadmium Ions Using Biomolecular Recognition
A selective, accurate, and sensitive
method for monitoring of cadmium
ions (Cd<sup>2+</sup>) based on a ratiometric electrochemical sensor
was developed, by simultaneously modifying with protoporphyrin IX
and 6-(ferroceney) hexanethiol (FcHT) on Au particle-deposited glassy
carbon electrode. On the basis of high affinity of biomolecular recognition
between protoporphyrin IX and Cd<sup>2+</sup>, the functionalized
electrode showed high selectivity toward Cd<sup>2+</sup> over other
metal ions such as Cu<sup>2+</sup>, Fe<sup>3+</sup>, Ca<sup>2+</sup>, and so on. Electroactive FcHT played the role as the inner reference
element to provide a built-in correction, thus improving the accuracy
for determination of Cd<sup>2+</sup> in the complicated environments.
The sensitivity of the electrochemical sensor for Cd<sup>2+</sup> was
enhanced by ∼3-fold through the signal amplification of electrodeposited
gold nanoparticles. Accordingly, the present ratiometric method demonstrated
high sensitivity, broad linear range from 100 nM to 10 μM, and
low detection limit down to 10 nM (2.2 ppb), lower than EPA and WHO
guidelines. Finally, the ratiometric electrochemical sensor was successfully
applied in the determination of Cd<sup>2+</sup> in water samples,
and the obtained results agreed well with those obtained by the conventional
ICP-MS method
Label-Free Electrochemical Biosensor for Monitoring of Chloride Ion in an Animal Model of Alzhemier’s Disease
The
potential damage of Alzheimer’s disease (AD) in brain
function has attracted extensive attention. As the most common anion,
Cl<sup>–</sup> has been indicated to play significant roles
in brain diseases, particularly in the pathological process of AD.
In this work, a label-free selective and accurate electrochemical
biosensor was first developed for real-time monitoring of Cl<sup>–</sup> levels in a mouse brain model of AD and rat brain upon global cerebral
ischemia. Silver nanoparticles (AgNPs) were designed and synthesized
as selective recognition element for Cl<sup>–</sup>, while
5′-MB-GGCÂGCGÂATTÂTT-SH-3′ (SH-DNA-MB,
MB = methylene blue) was selected as an inner reference molecule for
a built-in correction to avoid the effects from the complicated brain.
The electrochemical biosensor showed high accuracy and remarkable
selectivity for determination of Cl<sup>–</sup> over other
anions, metal ions, amino acids, and other biomolecules. Furthermore,
three-dimensional nanostructures composed of single-walled carbon
nanotubes (SWNTs) and Au nanoleaves were assembled on the carbon fiber
microelectrode (CFME) surface to enhance the response signal. Finally,
the developed biosensor with high analytical performance, as well
as the unique characteristic of CFME itself including inertness in
live brain and good biocompatibility, was successfully applied to
in vivo determination of Cl<sup>–</sup> levels in three brain
regions: striatum, hippocampus, and cortex of live mouse and rat brains.
The comparison of average levels of Cl<sup>–</sup> in normal
striatum, hippocampus, and cortex of normal mouse brains and those
in the mouse model brains of AD was reported. In addition, the results
in rat brains followed by cerebral ischemia demonstrated that the
concentrations of Cl<sup>–</sup> decreased by 19.8 ± 0.5%
(<i>n</i> = 5) in the striatum and 27.2 ± 0.3% (<i>n</i> = 5) in hippocampus after cerebral ischemia for 30 min,
but that negligible change in Cl<sup>–</sup> concentration
was observed in cortex
Two-Photon Ratiometric Fluorescence Probe with Enhanced Absorption Cross Section for Imaging and Biosensing of Zinc Ions in Hippocampal Tissue and Zebrafish
Zinc ion (Zn<sup>2+</sup>) not only plays an important function
in the structural, catalytic, transcription, and regulatory of proteins,
but is also an essential ionic signal to regulate brain neurotransmitters
pass process. In this work, we designed and synthesized an intramolecular
charge transfer-based ratiometric two-photon fluorescence probe, P–Zn,
for imaging and biosensing of Zn<sup>2+</sup> in live cell, hippocampal
tissue, and zebrafish. The developed probe demonstrated high two-photon
absorption cross section (δ) of 516 ± 77 GM, which increased
to 958 ± 144 GM after the probe was coordinated with Zn<sup>2+</sup>. Furthermore, this P–Zn probe quickly recognized Zn<sup>2+</sup> with high selectivity, over other metal ions, amino acids, and reactive
oxygen species. More interestingly, the initial emission peak of the
present probe at 465 nm decreased with a new peak increased at 550
nm, leading to the ratiometric determination of Zn<sup>2+</sup> with
high accuracy. Finally, this two-photon fluorescence probe with high
temporal resolution and remarkable analytical performance, as well
as low-cytotoxicity, was successfully applied in imaging of live cells,
hippocampal tissues, and zebrafishes. The present P–Zn probe
combined with FLIM provided accurate mapping of Zn<sup>2+</sup> distribution
at single-cell level. More interestingly, the two-photon spectroscopic
results demonstrated that the level of Zn<sup>2+</sup> in hippocampal
tissue of mouse with AD was higher than that in normal mouse brain
A Single Nanoprobe for Ratiometric Imaging and Biosensing of Hypochlorite and Glutathione in Live Cells Using Surface-Enhanced Raman Scattering
Hypochlorite (ClO<sup>–</sup>) and glutathione (GSH) have
been reported to closely correlate with oxidative stress and related
diseases; however, a clear mechanism is still unknown, mainly owing
to a lack of accurate analytical methods for live cells. Herein we
create a novel surface-enhanced Raman scattering (SERS) nanoprobe,
4-mercaptophenol (4-MP)-functionalized gold flowers (AuF/MP), for
imaging and biosensing of ClO<sup>–</sup> and GSH in RAW 264.7
macrophage cells upon oxidative stress. The SERS spectra of AuF/MP
change with the reaction between ClO<sup>–</sup> and 4-MP on
AuFs within 1 min and then recover after reaction with GSH, resulting
in the ratiometric detection of ClO<sup>–</sup> and GSH with
high accuracy. The single SERS probe also shows high selectivity for
ClO<sup>–</sup> and GSH detection against other reactive oxygen
species and amino acids which may exist in biological systems, as
well as remarkable sensitivity ascribed to a larger amount of hot
spots on AuFs. The significant analytical performance of the developed
nanoprobe, together with good biocompatibility and high cell-permeability,
enables the present SERS probe imaging and real-time detection of
ClO<sup>–</sup> and GSH in live cells upon oxidative stress
Single Probe for Imaging and Biosensing of pH, Cu<sup>2+</sup> Ions, and pH/Cu<sup>2+</sup> in Live Cells with Ratiometric Fluorescence Signals
It
is very essential to disentangle the complicated inter-relationship
between pH and Cu in the signal transduction and homeostasis. To this
end, reporters that can display distinct signals to pH and Cu are
highly valuable. Unfortunately, there is still no report on the development
of biosensors that can simultaneously respond to pH and Cu<sup>2+</sup>, to the best of our knowledge. In this work, we developed a single
fluorescent probe, AuNC@FITC@DEAC (AuNC, gold cluster; FITC, fluorescein
isothiocyanate; DEAC, 7-diethylaminocoumarin-3-carboxylic acid), for
biosensing of pH, Cu<sup>2+</sup>, and pH/Cu<sup>2+</sup> with different
ratiometric fluorescent signals. First, 2,2′,2″-(2,2′,2″-nitrilotrisÂ(ethane-2,1-diyl)ÂtrisÂ((pyridin-2-yl-methyl)Âazanediyl))Âtriethanethiol
(TPAASH) was designed for specific recognition of Cu<sup>2+</sup>,
as well as for organic ligand to synthesize fluorescent AuNCs. Then,
pH-sensitive molecule, FITC emitting at 518 nm, and inner reference
molecule, DEAC with emission peak at 472 nm, were simultaneously conjugated
on the surface of AuNCs emitting at 722 nm, thus, constructing a single
fluorescent probe, AuNC@FITC@DEAC, to sensing pH, Cu<sup>2+</sup>,
and pH/Cu<sup>2+</sup> excited by 405 nm light. The developed probe
exhibited high selectivity and accuracy for independent determination
of pH and Cu<sup>2+</sup> against reactive oxygen species (ROS), other
metal ions, amino acids, and even copper-containing proteins. The
AuNC-based inorganic–organic probe with good cell-permeability
and high biocompatibility was eventually applied in monitoring both
pH and Cu<sup>2+</sup> and in understanding the interplaying roles
of Cu<sup>2+</sup> and pH in live cells by ratiometric multicolor
fluorescent imaging
Carbon-Dot-Based Ratiometric Fluorescent Probe for Imaging and Biosensing of Superoxide Anion in Live Cells
In
this article, a ratiometric fluorescent biosensor for O<sub>2</sub><sup>•–</sup> was developed, by employing carbon dots
(C-Dots) as the reference fluorophore and hydroethidine (HE), a specific
organic molecule toward O<sub>2</sub><sup>•–</sup>,
playing the role as both specific recognition element and response
signal. The hybrid fluorescent probe CD-HE only emitted at 525 nm
is ascribed to C-Dots, while HE was almost nonfluorescent, upon excitation
at 488 nm. However, after reaction with O<sub>2</sub><sup>•–</sup>, a new emission peak ascribed to the reaction products of HE and
O<sub>2</sub><sup>•–</sup> was clearly observed at 610
nm. Meanwhile, this peak gradually increased with the increasing concentration
of O<sub>2</sub><sup>•–</sup> but the emission peak
at 525 nm stayed constant, leading to a ratiometric detection of O<sub>2</sub><sup>•–</sup>. The inorganic–organic
fluorescent sensor exhibited high sensitivity, a broad dynamic linear
range of ∼5 × 10<sup>–7</sup>–1.4 ×
10<sup>–4</sup> M, and low detection limit down to 100 nM.
The present probe also showed high accuracy and excellent selectivity
for O<sub>2</sub><sup>•–</sup> over other reactive oxygen
species (ROS), metal ions, and so on. Moreover, the C-Dot-based inorganic–organic
probe demonstrated long-term stability against pH changes and continuous
light illumination, good cell-permeability, and low cytotoxicity.
Accordingly, the developed fluorescent biosensor was eventually applied
for intracellular bioimaging and biosensing of O<sub>2</sub><sup>•–</sup> changes upon oxidative stress
Bioimaging and Biosensing of Ferrous Ion in Neurons and HepG2 Cells upon Oxidative Stress
Iron ions, as a main
component of intracellular labile iron, not
only play an important function in oxygen transport, enzymatic reactions,
and electron transport but also are vitally important in oxidative
stress. In this work, we developed a ratiometric fluorescent biosensor
for ferrous ion (Fe<sup>2+</sup>), in which gold nanoclusters (AuNCs)
were synthesized as a stable fluorescent probe and a ligand (FeL)
was designed for specific recognition of Fe<sup>2+</sup> and conjugated
onto AuNCs (AuNC@FeL). Meanwhile, water-soluble sulfocyanine 7 <i>N</i>-hydroxysuccinimide ester (Cy7 NHS ester) was immobilized
onto AuNC@FeL as a reference element. The developed ratiometric fluorescent
nansosensor displayed good linearity with the concentration of Fe<sup>2+</sup> in the range of 1–105 μM, and detection limit
was achieved down to 210 nM. In addition, this nanosensor responded
to Fe<sup>2+</sup> in less than 1.23 s and showed high selectivity
against other metal ions, amino acids, and reactive oxygen species.
With the advantages of high selectivity and accuracy, as well as quick
response and long-term stability, this organic–inorganic ratiometric
fluorescent probe was successfully applied in real-time biosensing
and bioimaging of Fe<sup>2+</sup> in neurons and HepG2 cells. By use
of this tool, it was found that the increasing concentration of Fe<sup>2+</sup> in live cells was closely related to oxidative stress
- …