Biosensor Probe Research Articles

Human umbilical artery endothelial cells from Large-for-Gestational-Age newborn have increased antioxidant efficiency and gene expression.

Obesity is a public health problem worldwide, and especially in women in reproductive age where more than one in three have obesity. Maternal obesity is associated with an increased maternal, placental, and newborn oxidative stress, which has been proposed as a central factor in vascular dysfunction in large-for-gestational-age (LGA) newborn. However, cellular and molecular mechanisms behind this effect have not been elucidated. Untreated human umbilical artery endothelial cells (HUAEC) from LGA (LGA-HUAEC) presented higher O2- levels, superoxide dismutase activity and heme oxygenase 1 messenger RNA (mRNA) levels, paralleled by reduced GSH:GSSG ratio and NRF2 mRNA levels. In response to an oxidative challenge (hydrogen peroxide), only HUAEC from LGA exhibited an enhanced Glutathione Peroxidase 1 (GPX1) expression, as well as a more efficient antioxidant machinery measured by the biosensor probe, HyPer. An open state of chromatin in the TSS region of GPX1 in LGA-HUAEC was evidenced by the DNase-HS assay. Altogether, our data indicate that LGA-HUAEC have an altered cellular and molecular antioxidant system. We propose that a chronic pro-oxidant intrauterine milieu, as evidenced in pregestational obesity, could induce a more efficient antioxidant system in fetal vascular cells, which could be maintained by epigenetic mechanism during postnatal life.

In Vivo High-resolution Ratiometric Fluorescence Imaging of Inflammation Using NIR-II Nanoprobes with 1550 nm Emission

Quantitatively imaging the spatiotemporal distribution of biological events in living organisms is essential to understand fundamental biological processes. Self-calibrating ratiometric fluorescent probes enable accurate and reliable imaging and sensing, but conventional probes using wavelength of 400-900 nm suffer from extremely low resolution for in vivo application due to the disastrous photon scattering and tissue autofluorescence background. Here, we develop a NIR-IIb (1500-1700 nm) emissive nanoprobe for high-resolution ratiometric fluorescence imaging in vivo. The obtained nanoprobe shows fast ratiometric response to hypochlorous acid (HOCl) with a detection limit down to 500 nM, through an absorption competition-induced emission (ACIE) bioimaging system between lanthanide-based downconversion nanoparticles and Cy7.5 fluorophores. Additionally, we demonstrate the superior spatial resolution of 1550 nm to a penetration depth of 3.5 mm in a scattering tissue phantom, which is 7.1-fold and 2.1-fold higher than that of 1064 and 1344 nm, respectively. With this nanoprobe, clear anatomical structures of lymphatic inflammation in ratiometric channel are observed with a precise resolution of ∼477 μm. This study will motivate the further research on the development of NIR-II probes for high-resolution biosensing in vivo.

Accelerated 19F·MRI Detection of Matrix Metalloproteinase-2/-9 through Responsive Deactivation of Paramagnetic Relaxation Enhancement.

Paramagnetic gadolinium ions (GdIII), complexed within DOTA-based chelates, have become useful tools to increase the magnetic resonance imaging (MRI) contrast in tissues of interest. Recently, “on/off” probes serving as 19F·MRI biosensors for target enzymes have emerged that utilize the increase in transverse (T 2 ∗ or T 2) relaxation times upon cleavage of the paramagnetic GdIII centre. Molecular 19F·MRI has the advantage of high specificity due to the lack of background signal but suffers from low signal intensity that leads to low spatial resolution and long recording times. In this work, an “on/off” probe concept is introduced that utilizes responsive deactivation of paramagnetic relaxation enhancement (PRE) to generate 19F longitudinal (T 1) relaxation contrast for accelerated molecular MRI. The probe concept is applied to matrix metalloproteinases (MMPs), a class of enzymes linked with many inflammatory diseases and cancer that modify bioactive extracellular substrates. The presence of these biomarkers in extracellular space makes MMPs an accessible target for responsive PRE deactivation probes. Responsive PRE deactivation in a 19F biosensor probe, selective for MMP-2 and MMP-9, is shown to enable molecular MRI contrast at significantly reduced experimental times compared to previous methods. PRE deactivation was caused by MMP through cleavage of a protease substrate that served as a linker between the fluorine-containing moiety and a paramagnetic GdIII-bound DOTA complex. Ultrashort echo time (UTE) MRI and, alternatively, short echo times in standard gradient echo (GE) MRI were employed to cope with the fast 19F transverse relaxation of the PRE active probe in its “on-state.” Upon responsive PRE deactivation, the 19F·MRI signal from the “off-state” probe diminished, thereby indicating the presence of the target enzyme through the associated negative MRI contrast. Null point 1H·MRI, obtainable within a short time course, was employed to identify false-positive 19F·MRI responses caused by dilution of the contrast agent.

Graphene oxide and gold nanoparticle based dual platform with short DNA probe for the PCR free DNA biosensing using surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) based DNA biosensors have considered as excellent, fast and ultrasensitive sensing technique which relies on the fingerprinting ability to produce molecule specific distinct spectra. Unlike conventional fluorescence based strategies SERS provides narrow spectral bandwidths, fluorescence quenching and multiplexing ability, and fitting attribute with short length probe DNA sequences. Herein, we report a novel and PCR free SERS based DNA detection strategy involving dual platforms and short DNA probes for the detection of endangered species, Malayan box turtle (MBT) (Cuora amboinensis). In this biosensing feature, the detection is based on the covalent linking of the two platforms involving graphene oxide-gold nanoparticles (GO-AuNPs) functionalized with capture probe 1 and gold nanoparticles (AuNPs) modified with capture probe 2 and Raman dye (Cy3) via hybridization with the corresponding target sequences. Coupling of the two platforms generates locally enhanced electromagnetic field ‘hot spot’, formed at the junctions and interstitial crevices of the nanostructures and consequently provide significant amplification of the SERS signal. Therefore, employing the two SERS active substrates and short-length probe DNA sequences, we have managed to improve the sensitivity of the biosensors to achieve a lowest limit of detection (LOD) as low as 10 fM. Furthermore, the fabricated biosensor exhibited sensitivity even for single nucleotide base-mismatch in the target DNA as well as showed excellent performance to discriminate closely related six non-target DNA sequences. Although the developed SERS biosensor would be an attractive platform for the authentication of MBT from diverse samples including forensic and/or archaeological specimens, it could have universal application for detecting gene specific biomarkers for many diseases including cancer.

DNA-NH<sub>2</sub> acylation reaction: Molecular weight or conformation dominates?

DNA has the unique chemical and physical characteristics as a carrier of genetic information. With the development of structural DNA nanotechnology, it has been recognized that DNA can perform versatile functions with promising applications in nanomachine, computing, sensing and nanoarchitectures. In addition, the chemical incorporation with various functional groups brings in a diverse range of additional properties to DNA molecules for broadened applications. Therefore, post-synthetic modification of DNA has been widely used to introduce additional functionalities to DNA molecules, for example, design and synthesis of DNA-encoded library, preparation of DNA-based probes for biosensing, improving binding activities of DNA aptamers, etc. The modification efficiency is determined by both the intrinsic factors of the molecules involved (DNA and reagents) and the external factors (experimental conditions). However, previous studies on the modification focused on the optimization of reaction conditions. To determine the important intrinsic factors that affect modification efficiency, we have conducted a systematic study on the reaction with a model system— acylation of amino-DNA. Nine amino-modified DNAs with two different DNA conformations (a–i) were reacted with two carboxylic acids with different molecule weights (12-oxo-2,5,8,11-tetraoxapentadecan-15-oic acid, M W 264.1209, and 30-oxo-2,5,8,11,14,17,20,23,26,29-decaoxatritriacontan-33-oic acid, M W 528.2782), respectively, and characterized by polyacrylamide gel electrophoresis (PAGE). The bands were analyzed and calculated by Image J . In the present study, three factors are considered for the design. First, acylation is one of the most widely methods used for chemical modifications of DNA. The acylation reactions afford amides and these amides binding to DNA form more structurally complex and diverse DNA building blocks. Therefore, we explored the acylation reaction between amino-modified DNA with carboxylic acids. Second, two DNA conformations (single-stranded random coils, ssDNAs, and rigid, double-stranded DNA duplexes, dsDNA) were included. Single-stranded DNAs are more flexible than rigid DNA duplexes and thus can provide more variability in terms of modulating orientation of the reaction group to facilitate reactions. Third, the two small organic molecules with a varying number of polyethylene glycol (PEG) units were used, because PEG has been widely used in the field of chemical modification of biomacromolecules due to its excellent properties including a wide range of solubility, predominant bio-compatibility, good stability, low toxicity and no irritation, etc. We, therefore, systematically studied the DNA modification reaction to investigate the influences of two intrinsic factors ( M W and conformation) on the reaction. The primary factor for DNA-NH2 acylation reaction is molecular weight ( M W). The higher the M W of the regents (both small molecules and DNAs) are, the slower the reactions are. DNA conformation plays a much minor role in the reaction. Compared with rigid dsDNA duplexes, flexible ssDNA chains facilitate reactions. Based on the current study, we would suggest for post-synthetic modification of DNA: (1) Keep the molecular weights of all reagents (both small molecules and DNA molecules) to the minimal in the design to allow fast diffusion. (2) Keep the DNA strands near the modification location to be single stranded to facilitate orientation adjustment. If high molecular weight and rigid conformation (duplex) are not avoidable, reaction time and/or reagent concentration should be elongated to ensure the modification efficiency.

Development of DNA Pair Biosensor for Quantization of Nuclear Factor Kappa B.

Nuclear factor kappa B (NF-κB), regulating the expression of several genes that mediate the inflammatory responses and cell proliferation, is one of the therapeutic targets for chronic inflammatory disease and cancer. A novel molecular binding scheme for the detection of NF-κB was investigated for its affinity to Ig-κB DNA composed by dye and quencher fluorophores, and this specificity is confirmed by competing with the DNA sequence that is complementary to the Ig-κB DNA. We create a normalization equation to remove the negative effects from the various initial fluorophore concentrations and the background noise. We also found that a periodic shaking at a frequency could help to stabilize the DNA–protein binding. The calibration experiment, using purified p50 (NF-κB), shows that this molecular probe biosensor has a detection limit on the order of nanomolar. The limit of detection is determined by the binding performance of dye and quencher oligonucleotides, and only a small portion of probes are stabilized by DNA-binding protein NF-κB. The specificity experiment also shows that p50/p65 heterodimer has the highest affinity for Ig-κB DNA; p65 homodimer binds with intermediate affinity, whereas p50 shows the lowest binding affinity, and Ig-κB DNA is not sensitive to BSA (bovine albumin serum). The experiment of HeLa nuclear extract shows that TNF-α stimulated HeLa nuclear extract has higher affinity to Ig-κB DNA than non-TNF-stimulated HeLa nuclear extract (4-h serum response). Therefore, the molecular binding scheme provides a rapid, quantitative, high throughput, and automated measurement of the DNA-binding protein NF-κB at low cost, which is beneficial for automated drug screening systems.

Dual-Aptamer-Conjugated Molecular Modulator for Detecting Bioactive Metal Ions and Inhibiting Metal-Mediated Protein Aggregation.

Bioactive metal ions play important roles in both physiological and pathological processes. Developing biosensing probes for bioactive metal ion detection can contribute to fields including disease diagnosis and therapy and studying the mechanisms of biological activities. In this work, we designed a dual-aptamer-conjugated molecular modulator that can detect Zn2+ and further inhibit Zn2+-induced amyloid β (Aβ) aggregation. The molecular modulator is able to selectively target Aβ species and block Zn2+ due to the specific recognition capability of aptamers. With the binding of Zn2+, the fluorescence signal of this molecular modulator is restored, thus allowing for Zn2+ detection. More importantly, this molecular modulator can inhibit the generation of Zn2+-triggered Aβ aggregates due to the trapping of Zn2+ around Aβ species. Circular dichroism measurements reveal that the dual-aptamer-conjugated molecular modulator prevents the conformational transition of the Aβ monomer from a random coil to a β-sheet. Furthermore, after treating with the molecular modulator, no Aβ aggregate is observed in the Aβ solution with added Zn2+, demonstrating that Aβ aggregation is successfully inhibited by this molecular modulator. Our approach provides a promising tool for detecting bioactive metal ions and studying the molecular mechanisms behind life activities.

Design considerations of a surface plasmon resonance (SPR) based tapered fiber optic bio-sensing probe with graphene-MoS2 over layers

In this paper, we have reported the design considerations of a surface plasmon resonance (SPR) based tapered fiber optic sensor by coating a thin film of platinum on a tapered fiber core followed by graphene-molybdenum disulphide (MoS2) monolayers. The theoretical study is based on five-layer matrix model. To see the effect of graphene-MoS2 over layers, performance parameters in terms of sensitivity and detection accuracy are evaluated for four taper profiles viz. exponential-linear, linear, parabolic and quadratic along with the taper ratio. From results, we inferred that with increase in taper ratio sensitivity also increases while detection accuracy decreases monotonically. For the proposed sensor configuration, maximum sensitivity value is found to be 7.04 μm/RIU at taper ratio 2.0 for exponential-linear taper profile while maximum detection accuracy obtained is 16.7623μm−1, at taper ratio 1.0. Thus, the results show that by introducing additional graphene-MoS2 monolayers, the sensitivity of the proposed sensing probe is enhanced by more than 44% at taper ratio 2 as compared to the conventionally used SPR based fiber optic sensors coated with platinum only. Also, the effect of increasing number of layers of graphene and MoS2 on the performance parameters is evaluated and compared. The advantageous features of the graphene and MoS2 layers have also been discussed for bio-sensing applications.

An enzyme-based electrochemical biosensor probe with sensitivity to detect astrocytic versus glioma uptake of glutamate in real time in vitro

Glutamate, a major excitatory neurotransmitter in the central nervous system, is essential for regulation of thought, movement, memory, and other higher functions controlled by the brain. Dysregulation of glutamate signaling is associated with severe neuropathological conditions, such as epilepsy, and glioma, a form of brain cancer. Glutamate signals are currently detected by several types of neurochemical probes ranging from microdialysis-based to enzyme-based carbon fiber microsensors. However, an important technology gap exists in the ability to measure glutamate dynamics continuously, and in real time, and from multiple locations in the brain, which limits our ability to further understand the involved spatiotemporal mechanisms of underlying neuropathologies. To overcome this limitation, we developed an enzymatic glutamate microbiosensor, in the form of a ceramic-substrate enabled platinum microelectrode array, that continuously, in real time, measures changes in glutamate concentration from multiple recording sites. In addition, the developed microbiosensor is almost four-fold more sensitive to glutamate than enzymatic sensors previously reported in the literature. Further analysis of glutamate dynamics recorded by our microbiosensor in cultured astrocytes (control condition) and glioma cells (pathological condition) clearly distinguished normal versus impaired glutamate uptake, respectively. These results confirm that the developed glutamate microbiosensor array can become a useful tool in monitoring and understanding glutamate signaling and its regulation in normal and pathological conditions. Furthermore, the developed microbiosensor can be used to measure the effects of potential therapeutic drugs to treat a range of neurological diseases.

Label-Free Thrombin Detection Using a Tapered Fiber-Optic Interferometric Aptasensor

Aptamer biosensor for label-free thrombin detection based on a tapered fiber-optic interferometer has been proposed and demonstrated. The biosensor probe can be easily fabricated by tapering a commercial double-cladding fiber down to 5 μm in diameter and it provides a high refractive index sensitivity of 1660 nm/RIU. The changes are determined by tracing the wavelength shift of the dip in the transmission spectrum with variable surrounding refractive index. With the help of the surface functionalization of thrombin-binding aptamers, the proposed fiber-optic biosensor proves its capability in label-free detection of thrombin with a lowest detectable concentration of 0.1 μm, together with high specificity in various concentrations of pure and mixed thrombin solutions.

Biofunctionalized two-dimensional Ti3C2 MXenes for ultrasensitive detection of cancer biomarker

In this work, ultrathin Ti3C2-MXene nanosheets were synthesized by minimally intensive layer delamination methods, and uniformly functionalized with aminosilane (f-Ti3C2-MXene) to provide a covalent binding for the immobilized bio-receptor (anti-CEA) for label free, ultrasensitive detection of cancer biomarker (carcinoembryonic antigen, CEA). The effect of different redox probes on the electrochemical behavior of f-Ti3C2-MXene was investigated and found that hexaammineruthenium ([Ru(NH3)6]3+) is the preferable redox probe for biosensing. The fabricated biofunctionalized Ti3C2-MXene exhibits a linear detection range of 0.0001–2000 ng mL−1 with sensitivity of 37.9 µA ng−1 mL cm−2 per decade. The wider linear detection range of our f-Ti3C2-MXene is not only higher than previously reported pristine 2D nanomaterials, but is even comparable to other hybrid 2D nanomaterials. We believe that this work opens a new window for development of MXene-based highly sensitive DNA, aptamer, enzyme, antibody, and cell based biosensors, and could be further used in drug delivery application.

Three-dimensional Tri-SNSs-layered electrodeposited reduced graphene oxide for ECL biosensing of DNA

In this study,we proposed a triangular silver nanosheets (Tri-SNSs)-layered, Chitosan (CS)-supported three-dimensional of reduced graphene oxide (3D-ERGO) electrochemiluminescence (ECL) biosensing platform using self-designed dual-Ru(bpy)32+ scDNA (Ru2-DNA) as capture probe for ECL biosensing of single-chain DNA (scDNA). Based on the different affinity with scDNA and double chain DNA (dcDNA), the biosensor is designed to recognize the target DNA (t-DNA), which leads to the desorption of a hybrid molecule from the surface of the biosensor, further removing the Ru2-DNA and inhibiting the ECL. Analytical results clearly showed that the electrochemical and ECL behaviors of proposed biosensing platform on the glassy carbon electrode (GCE) exhibited outstanding performance, which was due to large specific surface area, high carrier mobility and strong π–π non-covalent attraction toward single-chain DNA (scDNA) of the stable 3D platform, and ECL amplification of Tri-SNSs. Besides, based on such a system, this strategy can effectively identify full match and mismatched target DNA (M-DNA) with a wide concentration range beyond 7 orders of magnitude and detection limit down to 16.2 aM. Therefore, the 3D biosensing strategy shows potential for the application of bioassays.

Fully electronic urine dipstick probe for combinatorial detection of inflammatory biomarkers.

Aim:An electrochemical urine dipstick probe biosensor has been demonstrated using molybdenum electrodes on nanoporous polyamide substrate for the quantitative detection of two inflammatory protein biomarkers, CRP and IL-6.Materials & methods:The electrode interface was characterized using ζ-potential and Fourier transform infrared spectroscopy. Detection of biomarkers was demonstrated by measuring impedance changes associated with the dose concentrations of the two biomarkers. A proof of feasibility of point-of-care implementation of the biosensor was demonstrated using a portable electronics platform.Results & conclusion:Limit of detection of 1 pg/ml was achieved for CRP and IL-6 in human urine and synthetic urine buffers. The developed portable hardware demonstrated close correlation with benchtop equipment results.

Long-Lived Emissive Probes for Time-Resolved Photoluminescence Bioimaging and Biosensing.

In this Review article, we systematically summarize the design and applications of various kinds of long-lived emissive probes for bioimaging and biosensing via time-resolved photoluminescence techniques. The probes reviewed, including lanthanides, transition-metal complexes, organic dyes, carbon and silicon nanoparticles, metal clusters, and persistent phosphores, exhibit longer luminescence lifetimes than that of autofluorescence from biological tissue and organs. When these probes are internalized into living cells or animals, time-gated photoluminescence imaging selectively collects long-lived signals for intensity analysis, while photoluminescence lifetime imaging reports the decay details of each pixel. Since the long-lived signals are differentiated from autofluorescence in the time domain, the imaging contrast and sensing sensitivity are remarkably improved. The future prospects and challenges in this rapidly growing field are addressed.

Graphene solution-gated field effect transistor DNA sensor fabricated by liquid exfoliation and double glutaraldehyde cross-linking

Graphene based solution-gated field effect transistors (G-SgFETs) have been extensively investigated as potential biosensors for various analytes. Liquid exfoliated graphene (LEG) is a recently developed economic and efficient carbon material, in comparison with graphene materials produced by other methods like Hummers, mechanical exfoliation and epitaxy. However, bio-sensitive and LEG based SgFETs (bioLEG-SgFETs) have not been demonstrated because of the deficiency in oxygen containing groups on LEG nano-sheets which are believed to be able to graft bio-sensing probes. Here, we describe a method for fabricating bioLEG-SgFETs and demonstrate their bio-application in single-strand DNA (ssDNA) detection, for the first time. The as-prepared LEG supernatant, deposited and functionalized films are thoroughly characterized by scanning electron microscopy, atom force microscopy, Raman and X-ray photoelectron spectroscopy. Furthermore, the feasibility of the proposed method is testified by the typical ambipolar transferring features possessed by G-SgFETs, as well as the ionic screening effect exhibited by the bio-modified G-SgFETs. BioLEG-SgFETs' performance acting as a sensor is evaluated by the detection of DNA hybridization, as proof-of-concept, which include target complementary ssDNA (csDNA), mismatched and half-matched ssDNA. The limit-of-detection for csDNA is about 10 fM. Accordingly, LEG would be a promising alternative for the traditional graphene materials used in G-SgFETs.

A ratiometric fluorescent probe for bioimaging and biosensing of HBrO in mitochondria upon oxidative stress.

A novel ratiometric fluorescent probe with high selectivity and sensitivity was designed and developed for bioimaging and biosensing of HBrO in mitochondria. Using this useful tool with low cytotoxicity and good biocompatibility, it was found that O2˙--induced oxidative stress triggered the burst of HBrO in mitochondria.

Target regulated photo induced electron transfer of DNA-Cu nanoparticles and their application for the detection of the hepatitis B gene

Despite the distinct features of polythymine (T)-templated copper nanoparticles (polyT-Cu NPs) as fluorescent probes for various biosensors, most of the reported methods involve labeling with an appropriate fluorescence quencher, or the addition of enzyme to digest the DNA-template.

Silicon quantum dots with tunable emission synthesized via one-step hydrothermal method and their application in alkaline phosphatase detection

Alkaline phosphatase (ALP) plays an important role in normal growth. Many diseases will occur if the content of ALP is abnormal. Hence, the development of convenient and sensitive assay for monitoring ALP is extremely important. In this work, hydrophilic silicon quantum dots (SiQDs) with tunable emission were synthesized via hydrothermal method. The fluorescent emission of SiQDs was changed easily by adjusting the pH value of reaction system. The detection of ALP activity has been developed by measuring the fluorescence quenching of SiQDs. Quantitative limited evaluation of ALP activity was 1 U/L and the linear relationship was 1 U/L to 7500 U/L. Meanwhile, the fluorescent of as-prepared SiQDs were stable in physiological environment and embodied an excellent anti-interference of ions. High sensitivity and wider detection range, the proposed assay is capable of proved that they could serve as a new species of fluorescence probes for biosensors.

Toward Universal SERS Detection of Disease Signaling Bioanalytes Using 3D Self-Assembled Nonplasmonic near-Quantum-Scale Silicon Probe

Currently, the quantum-scale surface-enhanced Raman scattering (SERS) properties of Si materials have yet to be discovered for universal biosensing applications. In this study, a potential universal biosensing probe is generated by activating the SERS functionality of Si nanostructures through near quantum-scale (nQS) engineering. We introduce herein 3D nonplasmonic Si nanomesh structure with nQS defects for SERS biosensing applications. Through ionization of a single-crystal defect-free Si wafer, highly defect-rich Si subnano-orbs (sNOs) are fabricated and self-assemble as connective 3D Si nanomesh structures with enhanced SERS biosensing activity. By amending the laser ionization and ion-ion interactions, we observe the controlled synthesis of engineered nQS defects in the form of nQS-grain boundary disorder or surface nQS voids within the interconnected Si sNOs. To our knowledge, it is shown here for the first time that defect-rich Si nanomesh structures exhibit enhanced Raman activity, with the nQS morphological and crystallographic defects acting as the prime SERS contributors without a plasmonic contribution. The SERS biosensing sensitivity with the synthesized defect-rich Si nanomesh structures without an additional plasmonic material was evaluated using of a tripeptide biomarker l-glutathione (GSH); we observe an enhancement factor value of ∼102 for the GSH biomolecules with 10-9 M sensitivity, a phenomena to our knowledge that has yet to be reported. Additionally, the SERS detection of multiple disease-signaling biomolecules (cysteine, tryptophan, and methionine) is achieved at very low analyte concentration (10-9 M). These results indicate a potential new dimension to universal SERS biosensing applications with these unique nonplasmonic defect-rich 3D nQS-Si nanostructures.

Facile synthesis of N-rich carbon quantum dots from porphyrins as efficient probes for bioimaging and biosensing in living cells.

N-rich metal-free and metal-doped carbon quantum dots (CQDs) have been prepared through one-step hydrothermal method using tetraphenylporphyrin or its transition metal (Pd or Pt) complex as precursor. The structures and morphology of the as-prepared nanoparticles were analyzed by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectra. Three kinds of nanocomposites show similar structures except for the presence of metal ions in Pd-CQDs and Pt-CQDs indicated by X-ray photoelectron spectroscopy. All of them display bright blue emission upon exposure to ultraviolet irradiation. The CQDs exhibit typical excitation-dependent emission behavior, with the emission quantum yield of 10.1%, 17.8%, and 15.2% for CQDs, Pd-CQDs, and Pt-CQDs, respectively. Moreover, the CQDs, Pd-CQDs, and Pt-CQDs could serve as fluorescent probes for the specific and sensitive detection of Fe3+ ions in aqueous solution. The low cytotoxicity of CQDs is demonstrated by MTT assay against HeLa cells. Therefore, the CQDs can be used as efficient probes for cellular multicolor imaging and fluorescence sensors for the detection of Fe3+ ions due to their low toxicity, excellent biocompatibility, and low detection limits. This work provides a new route to synthesize highly luminescent N-rich metal-free or metal-doped CQDs for multifunctional applications.