Detection Of HIV-1 DNA Research Articles

Efficient fluorescence quenching and low-limit detection of HIV-1 DNA via morphology controlled ZIF-8 crystals

ZIF-8 (zinc-methylimidazolate framework-8) has shown promising applications as a fluorescence sensing platform, particularly in fluorescence quenching sensors for various biological and chemical analyses and detections. However, the impact of the morphology of ZIF-8 crystals on their performance of biomolecule detection, especially DNA detection, remains to be explored. In this study, six types of ZIF-8 crystals with different morphology (cubic, rough octahedral, flakes, rhombic, dodecahedral, and hexapod) are successfully synthesized by incorporating different concentrations of the surfactant/end-capping agent, namely cetyltrimethylammonium bromide (CTAB) and/or tris(hydroxymethyl)aminomethane (TRIS). These crystals are characterized in terms of morphology, crystal structure, specific surface area, and electrostatic adsorption capacity. Subsequently, these morphologically different ZIF-8 crystals are combined with fluorophore carboxyfluorescein (FAM)-labeled single-stranded DNA (ss-DNA) to form FAM-DNA@ZIF-8 biosensor. Then, their fluorescence quenching efficiency is characterized by using the fluorescence spectroscopy. The measurement results show that, due to its higher external specific surface area and zeta potential thereby higher electrostatic adsorption capacity, the cubic ZIF-8 crystal can effectively capture more FAM-DNA molecules through the electrostatic adsorption and achieve high fluorescence quenching efficiency via the fluorescence resonance energy transfer mechanism. Thus, the fluorescence quenching efficiency of the cubic FAM-DNA@ZIF-8 reaches up to 98.1 %. Finally, the cubic FAM-DNA@ZIF-8 biosensor is used to detect the complementary target HIV-1 DNA via the fluorescence recovery. The experimental results show that the fluorescence recovery efficiency of the FAM-DNA@ZIF-8 reaches up to 40.8 upon the addition of complementary target ssDNA, significantly higher than the recovery efficiency when non-complementary target DNA is introduced. Also, both fluorescence quenching efficiency and recovery efficiency of the cubic FAM-DNA@ZIF-8 are much higher than those of the reported biosensors based on ZIF-8 crystals with non-optimal morphology. Additionally, the fluorescence recovery sensitivity of the biosensor is 0.536/(nM⋅mL), with a detection limit as low as 1.37 nM. In addition, its detection performance remains almost unchanged after ten days of storage. These findings provide valuable insights for optimizing ZIF-8-based DNA biosensor.

Coreactant-Free Zirconium Metal-Organic Framework with Dual Emission for Ratiometric Electrochemiluminescence Detection of HIV DNA.

Owing to the limitations of dual-signal luminescent materials and coreactants, constructing a ratiometric electrochemiluminescence (ECL) biosensor based on a single luminophore is a huge challenge. This work developed an excellent zirconium metal-organic framework (MOF) Zr-TBAPY as a single ECL luminophore, which simultaneously exhibited cathodic and anodic ECL without any additional coreactants. First, Zr-TBAPY was successfully prepared by a solvothermal method with 1,3,6,8-tetra(4-carboxyphenyl)pyrene (TBAPY) as the organic ligand and Zr4+ cluster as the metal node. The exploration of ECL mechanisms confirmed that the cathodic ECL of Zr-TBAPY originated from the pathway of reactive oxygen species (ROS) as the cathodic coreactant, which is generated by dissolved oxygen (O2), while the anodic ECL stemmed from the pathway of generated Zr-TBAPY radical itself as the anodic coreactant. Besides, N,N-diethylethylenediamine (DEDA) was developed as a regulator to ECL signals, which quenched the cathodic ECL and enhanced the anodic ECL, and the specific mechanisms of its dual action were also investigated. DEDA can act as the anodic coreactant while consuming the cathodic coreactant ROS. Therefore, the coreactant-free ratiometric ECL biosensor was skillfully constructed by combining the regulatory role of DEDA with the signal amplification reaction of catalytic hairpin assembly (CHA). The ECL biosensor realized the ultrasensitive ratio detection of HIV DNA. The linear range was 1 fM to 100 pM, and the limit of detection (LOD) was as low as 550 aM. The outstanding characteristic of Zr-TBAPY provided new thoughts for the development of ECL materials and developed a new way of fabricating the coreactant-free and single-luminophore ratiometric ECL platform.

Prevalence of detectable HIV-DNA and HIV-RNA in cerebrospinal fluid of youth with perinatal HIV and impaired cognition on antiretroviral therapy.

Central nervous system (CNS) HIV infection can impact cognition and may be an obstacle to cure in adolescents and young adults with perinatal HIV (AYAPHIV). IMPAACT2015 enrolled AYAPHIV on suppressive antiretroviral therapy (ART) with cognitive impairment to detect and quantify HIV in blood and cerebrospinal fluid (CSF). IMPAACT2015 was a U.S.-based multi-site, exploratory, observational study. Cognitive impairment was defined as NIH Toolbox Fluid Cognition Composite score (FCCS) more than 1 standard deviation below age-adjusted normative group mean. Cell-free HIV-RNA and cell-associated HIV pol/gag -DNA and 10 biomarkers of inflammation/neuronal injury were measured in paired CSF and blood. ART exposure concentrations were quantified in hair. Among 24 participants, 20 had successful CSF collection and 18 also met viral suppression criteria. Nine of 18 (50%) were female sex-at-birth, and 14 of 18 (78%) were black. Median (range) age was 20 years (13-27), time on ART was 18.3 years (8.0-25.5), and FCCS was 68 (53-80). HIV-DNA was detected in PBMCs from all participants. In CSF, two of 18 (11%, 95% CI: 1.4-34.7%) participants had detectable cell-free HIV-RNA, while HIV gag or pol -DNA was detectable in 13 of 18 (72%, 95% confidence interval: 47-90). Detectable HIV-DNA in CSF was associated with male sex-at-birth ( P = 0.051), lower CD4 + cell count at enrollment ( P = 0.016), and higher PBMC HIV pol -DNA copies ( P = 0.058). Hair antiretroviral concentrations and biomarkers were not associated with CSF HIV-DNA detection. We found that a high proportion of AYAPHIV with neurocognitive impairment had CSF cells harboring HIV-DNA during long-term virologic suppression. This evidence of persistent HIV-DNA in CSF suggests that the CNS should be considered in treatment and cure studies.

Virological safety of the UK blood supply in the era of individual risk assessments and HIV PrEP.

A more individualised donor selection policy was implemented in the UK in 2021, which replaced the previous 3-month deferral for men who have sex with men (MSM). Other blood services have a variety of policies in place to ensure the virological safety of blood components, ranging from an indefinite ban on MSM, to a defined period of exclusion, or to an individualised risk assessment that is not based on gender or sexual orientation. Justification of these policies should be based on scientific evidence including assessment of lengths of virological window periods, infectious disease epidemiology within donor populations and donation screening assay sensitivities. Developments in molecular technology and assays which can detect both antibodies and antigens in the very early stages of infection have significantly reduced the risk in most developed countries. However, the increasing usage of pre-exposure prophylaxis (PrEP) to prevent acquisition of HIV infection after possible high-risk sexual contact within the UK blood donor population has been recently noted. It has brought with it new diagnostic challenges within blood screening, notably possible non-detection of HIV RNA and serological markers following PrEP use despite potential infectivity. The use of other testing strategies such as detection of HIV DNA and screening for non-declared PrEP usage should be investigated further.

Automated and label-free detection of HIV DNA via digital microfluidics-chemiluminescence analysis

Automated and sensitive detection of nucleic acid is crucial for reliable and safe disease diagnostics because the minimum manual operation can effectively avoid sample contamination and infection risk. Herein, a sensitive, label-free and automated method was developed for detecting trace DNA by integrating digital microfluidics (DMF) with chemiluminescence (CL) detection. DMF can automatically manipulate discrete droplets. Taking advantage of sensitive and simple CL detection, DMF-CL integration can automatically and sensitively detect HIV DNA via the preset pathway. To further improve the sensitivity, on-chip exponential amplification reaction (EXPAR) was explored to produce large quantities of double-stranded DNA (dsDNA) in the presence of HIV DNA. Then, SYBR Green I (SG) intercalated into dsDNA to generate singlet oxygen upon light irradiation, which in situ oxidized potassium ferrocyanide into potassium ferricyanide. Finally, the CL reaction of potassium ferricyanide and luminol ensured the label-free, reliable and specific detection of HIV DNA in the range of 10 pM to 2 nM. Saving time-consuming and laborious manual operations, the DMF-CL integration greatly reduced the reagent consumption and avoided the contamination of DNA sample as well. Therefore, DMF-CL offers a promising and useful technology for developing automated and reliable biosensing and bioanalysis.

A facile enzyme-assisted multiple recycling amplification strategy for ultrasensitive fluorescence detection of HIV-1 DNA

We developed an enzyme-assisted multiple signal amplification reaction for target nucleic acid detection. In this strategy, the target nucleic acid as triggers, and in the presence of two specific primers, DNA polymerase and DNA nicking endonuclease act in concert to promote the repetitive cycle DNA replication process, leading to an exponential increase in nucleic acid sequence. Both ends of each sequence of the amplification products and the specific primer could from a unit of Mg2+-DNAzyme which in the presence of cofactor Mg2+ could recognize and cyclically cleave the hairpin probes in the solution and thus realize real-time fluorescence detection of HIV-1 DNA. Under optimal conditions, the detection limit of this method is 10−17 M. The simple in design, isothermal conditions and easy fluorescence measurement of this method exhibits superior sensitivity and specificity, and thus holds great potential to be a promising assay for quantitative detection of DNA or RNA in theoretical and clinic studies.

Gold nanocubes based optical detection of HIV-1 DNA via surface enhanced Raman spectroscopy

Optical detection of HIV-1 DNA with surface enhanced Raman spectroscopy (SERS) is a quick and versatile method, having great potential in screening and characterization of HIV-1 virus particle. We have synthesized and applied novel gold nanocubes (AuNCs) for signal enhancement of SERS to study HIV-1 DNA strands by taking into account the specific vibrational bands of functional groups. Raman peaks at 562 cm−1, 800 cm−1, 1094 cm−1 were observed in both Human Random Control DNA and HIV-1 DNA, while three new peaks were detected in infected DNA at 421 cm−1, 1069 cm−1 and 1254 cm−1. Raman bands in case of AuNCs coated HIV-1 DNA molecules were observed with enhanced intensity values as compared to the silver nanoparticles-based SERS substrate. In case of silver nanoparticles (AgNPs) conjugate DNA, we get all signatures of HIV-1 virus at almost the same position with peak distortions, peak alterations and intensities reductions. We overall molecularly observed HIV-1 infected DNA and Human Random Control DNA, with high sensitivity and selectivity using highly sensitive and stable AuNCs in SERS. This technique can be utilized to identify molecular structures and chemical identification of biomacromolecules which can further be investigated as biomarkers for the screening of whole-body HIV-1 virus particles.

HIV silencing and cell survival signatures in infected T cell reservoirs

Rare CD4 T cells that contain HIV under antiretroviral therapy represent an important barrier to HIV cure1–3, but the infeasibility of isolating and characterizing these cells in their natural state has led to uncertainty about whether they possess distinctive attributes that HIV cure-directed therapies might exploit. Here we address this challenge using a microfluidic technology that isolates the transcriptomes of HIV-infected cells based solely on the detection of HIV DNA. HIV-DNA+ memory CD4 T cells in the blood from people receiving antiretroviral therapy showed inhibition of six transcriptomic pathways, including death receptor signalling, necroptosis signalling and antiproliferative Gα12/13 signalling. Moreover, two groups of genes identified by network co-expression analysis were significantly associated with HIV-DNA+ cells. These genes (n = 145) accounted for just 0.81% of the measured transcriptome and included negative regulators of HIV transcription that were higher in HIV-DNA+ cells, positive regulators of HIV transcription that were lower in HIV-DNA+ cells, and other genes involved in RNA processing, negative regulation of mRNA translation, and regulation of cell state and fate. These findings reveal that HIV-infected memory CD4 T cells under antiretroviral therapy are a distinctive population with host gene expression patterns that favour HIV silencing, cell survival and cell proliferation, with important implications for the development of HIV cure strategies.

A Bioluminescent Protein-Graphene Oxide Donor-Quencher Pair in DNA Hybridization Assays.

Despite fluorescent quenching with graphene oxide (GO) having shown great success in various applications - bioluminescent quenching has not yet been demonstrated using GO as a quencher. To explore the ability of GO to quench bioluminescence, we used Gaussia luciferase (Gluc) as a donor and GO as a quencher and demonstrated its application in sensing of two target analytes, HIV-1 DNA and IFN-γ. We demonstrated that the incubation of Gluc conjugated HIV-1 and IFN-γ oligonucleotide probes with GO provided for monitoring of probe-target interactions based on bioluminescence measurement in a solution phase sensing system. The limits of detection obtained for IFN-γ and HIV-1 DNA detection were 17 nM and 7.59 nM, respectively. Both sensing systems showed selectivity toward the target analyte. The detection of IFN-γ in saliva matrix was demonstrated. The use of GO as a quencher provides for high sensitivity while maintaining the selectivity of designed probes to their respective targets. The use of GO as a quencher provides for an easy assay design and low cost, environmentally friendly reporter.

An ultrasensitive electrochemical DNA biosensor based on the highly conductive Nd–Sb-co-doped SnO2@Pt nanocomposite for the rapid detection of HIV-DNA

An ultrasensitive electrochemical DNA biosensor based on the highly conductive Nd–Sb-co-doped SnO2@Pt nanocomposite for the rapid detection of HIV-DNA

CRISPR-Cas12a-activated palindrome-catalytic hairpin assembly for ultrasensitive fluorescence detection of HIV-1 DNA

Accurate analysis of HIV DNA is valuable for the diagnosis of AIDS. Herein, an ultrasensitive and specific fluorescence method was developed for HIV-1 DNA detection based on CRISPR-Cas12a-activated palindrome-catalytic hairpin assembly (CRISPR-Cas12a-PCHA). The presence of HIV-1 DNA activated the trans-cleavage activity of CRISPR-Cas12a, which could continuously digest the DNA fragment of hairpins connected to magnetic beads to expose single-stranded RNA. After magnetic separation, the exposed RNA triggered multiple PCHA reactions, generating many Y-shaped DNA structures that were self-assembled into the DNA superstructures via the hybridization of palindromic sticky ends, leading to the release of amounts of fluorescence signal. Different from the reported recently biosensing strategies of nucleic acid amplification technologies-activated CRISPR-Cas12a, CRISPR-Cas12a-PCHA endowed the strategy with unique advantages of simple sample pretreatment, direct duplex target detection, and ultrahigh sensitivity. The strategy was able to resist the interference of the complex matrix in real sample and distinguish between HIV patients and healthy persons. Thus, the method is a promising tool for ultrasensitive and specific detection of HIV-1 DNA for AIDS diagnosis.

Electrochemical biosensor based on topological insulator Bi2Se3 tape electrode for HIV-1 DNA detection.

A large-size Bi2Se3 tape electrode (BTE) was prepared by peeling off a 2 × 1 × 0.5cm high-quality single crystal. The feasibility of using the flexible BTE as an efficient bioplatform to load Au nanoparticles and probe DNA for HIV-1 DNA electrochemical sensing was explored. Differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) show that the resultant biosensor has a wide linear range from 0.1 fM to 1pM, a low detection limit of 50 aM, excellent selectivity, reproducibility and stability, and is superior to the pM DNA detection level of Pt-Au, graphene-AuNPs hybrid biosensors. This outstanding performance is attributed to the intrinsic surface state of Bi2Se3 topological insulator in facilitating electron transfer. Therefore, BTE electrochemical biosensor platform has great potential in the application for sensitive detection of DNA biomarkers.

Label- and enzyme-free plasmon-enhanced single molecule fluorescence detection of HIV DNA fragments based on a catalytic hairpin assembly.

We developed a label- and enzyme-free single molecule fluorescence counting strategy for HIV DNA fragments detection. The nucleic acid biosensor consists of a 5' terminal connected with a triangular gold nanoplate, 3' terminal rich in guanine hairpin probe (HP1) and a hairpin probe HP2 complementary to the partial sequence of HP1. Without the existence of the target DNA, the DNA fragment rich in the guanine region is locked in a hairpin structure and cannot form a G-quadruplex, hence NMM exhibits a low fluorescence signal. When the target DNA exists, the hairpin assembly will trigger a strand displacement amplification reaction that produces a great number of G-quadruplexes, and the fluorescence brightness of NMM will be enhanced. The plasmon resonance effect of the triangular gold nanoplates will further amplify the fluorescence signal. This method can analyze the target DNA with high sensitivity and selectivity, and the detection limit is 0.83 fM. The analysis of the HIV DNA fragments in diluted human serum samples was successfully achieved, and the recovery rate was 92%-104%. Because of its easy operation and low cost, it has broad development potential in biochemical analysis and clinical applications.

Multiparameter immunohistochemistry analysis of HIV DNA, RNA and immune checkpoints in lymph node tissue

The main barrier to a cure for HIV is the persistence of long-lived and proliferating latently infected CD4+ T-cells despite antiretroviral therapy (ART). Latency is well characterized in multiple CD4+ T-cell subsets, however, the contribution of regulatory T-cells (Tregs) expressing FoxP3 as well as immune checkpoints (ICs) PD-1 and CTLA-4 as targets for productive and latent HIV infection in people living with HIV on suppressive ART is less well defined. We used multiplex detection of HIV DNA and RNA with immunohistochemistry (mIHC) on formalin-fixed paraffin embedded (FFPE) cells to simultaneously detect HIV RNA and DNA and cellular markers. HIV DNA and RNA were detected by in situ hybridization (ISH) (RNA/DNAscope) and IHC was used to detect cellular markers (CD4, PD-1, FoxP3, and CTLA-4) by incorporating the tyramide system amplification (TSA) system. We evaluated latently infected cell lines, a primary cell model of HIV latency and excisional lymph node (LN) biopsies collected from people living with HIV (PLWH) on and off ART. We clearly detected infected cells that coexpressed HIV RNA and DNA (active replication) and DNA only (latently infected cells) in combination with IHC markers in the in vitro infection model as well as LN tissue from PLWH both on and off ART. Combining ISH targeting HIV RNA and DNA with IHC provides a platform to detect and quantify HIV persistence within cells identified by multiple markers in tissue samples from PLWH on ART or to study HIV latency.

Detection of HIV/HCV virus DNA with homogeneous DNA machine-triggered in situ formation of silver nanoclusters

Currently, the early disease screening is still the most effective way to increase the survival rate of the HIV/HCV infected patients. However, the trace analysis remains a great challenge for early disease screening. Herein, a novel silver nanocluster (AgNCs) is in situ generated and served as fluorescence probes for the ultrasensitive HIV/HCV DNA detection by combing Exo III-assisted target recycling amplification (ERA) with rolling circle amplification (RCA). As an important key element of this sensor, the padlock probes (PLP) of RCA are exquisitely designed to compose of a guanine-rich (G-rich) region. Target DNA firstly hybridizes with the stem segment of the hairpin DNA (hp-DNA) and triggered the Exo III digestion, which releases and recycles the target and generate numerous ssDNA fragments. The generated ssDNA fragments act as ligation probes, which hybridize with PLP to trigger the RCA process, generating numerous periodically repeated cytosine-rich (C-rich) units. In the presence of NaBH4 and AgNO3, numerous AgNCs are in situ generated, thereby producing a strong fluorescent signal. Under optimal conditions, an ultrasensitive DNA machine is constructed for the detection of HIV DNA with a detection limit of 1.4 fM and a linear range of 10 fM to 100 pM. More fascinatingly, this DNA machine could intelligently distinguish multiple virus DNAs by the construction of analog AND and OR logic circuits.

Brief Report: Herpes Simplex Virus Type-2 Shedding and Genital Ulcers During Early HIV in Zimbabwean Women.

Herpes simplex virus type-2 (HSV-2) seropositive persons have a 3- to 5-fold higher risk of acquiring HIV, possibly because of HSV-2-induced inflammation and recruitment of susceptible immune cells to exposure sites. We hypothesized that cervical HSV-2 activation (ie, viral DNA shedding and/or ulcers) preceded HIV acquisition in the hormonal contraception and HIV cohort. Zimbabwean women who acquired HIV were matched to HIV-negative women on visit, age, and bacterial sexually transmitted infections. Up to 5 cervical swabs bracketing first polymerase chain reaction detection of HIV DNA (the index visit) were selected (t-6months, t-3months, tindex, t+3months, t+6months). Women with HSV-2 immunoglobulin G+ before tindex were polymerase chain reaction tested for viral shedding. Self-reported and clinician-diagnosed ulcers were documented. Multivariable logistic regression, accounting for matching, estimated adjusted odds ratios (aOR) and 95% confidence intervals (CIs) at each visit. Of 387 HSV-2 seropositive women, most had prevalent as compared with incident HSV-2 (91% vs. 9%, respectively). HSV-2 viral shedding was more common among HIV seroconverters than HIV-negative women (26% vs. 14%, P < 0.01). Shedding occurred around HIV acquisition (t-3months aOR, 2.7; 95% CI, 0.8 to 8.8; tindex aOR, 2.6; 95% CI, 1.1 to 6.5; t+3months aOR, 2.6; 95% CI, 1.0 to 6.6). Genital ulcers were reported more often among HIV seroconverters than HIV-negative women (13% vs. 7%; P = 0.06) and detection was after HIV acquisition (t+6months aOR, 14.5; 95% CI, 1.6 to 133.9). HSV-2 shedding appeared synergistic with HIV acquisition followed by presentation of ulcers. Evaluating all sexually transmitted infections rather than HSV-2 alone may clarify the relationship between inflammation and HIV acquisition.

Zettomole electrochemical HIV DNA detection using 2D DNA-Au nanowire structure, hemin/G-quadruplex and polymerase chain reaction multi-signal synergistic amplification

Multi-signal synergistically amplified electrochemical sensing of HIV DNA was proposed based on two-dimensional (2D) DNA-Au nanowire structure coupled with hemin/G-quadruplex and polymerase chain reaction (PCR). In the design, by using target HIV DNA as the template, PCR generated numbers of double-stranded DNA (dsDNA) with free single-stranded DNA (ssDNA) tails on one side and free G-quadruplex sequences on the other side. Then, the ssDNA tails of the PCR products were hybridized with the capture probe (CP) to introduce the hemin/G-quadruplex to the electrode surface as a redox-active reporter and to amplify the electrochemical signal as mimic peroxidase catalysis in the presence of H2O2. Meanwhile, (+)AuNPs were electrostatically adsorbed onto dsDNA surface for the formation of 2D DNA-Au nanowire structure, amplifying the electrochemical signal further as another mimic peroxidase and electric conductor together. By effectively combining these signal amplification processes, ultrasensitive HIV DNA detection was achieved with a detection limit of 1.3 aM, indicating that it has potential application in clinical diagnosis.

Nanosurface energy transfer indicating Exo III-propelled stochastic 3D DNA walkers for HIV DNA detection.

DNA-based nanomachines have aroused tremendous interest because of their potential applications in bioimaging, biocomputing, and diagnostic treatment. Herein, we constructed a novel exonuclease III-propelled and signal-amplified stochastic DNA walker that autonomously walked on a spherical particle-based 3D track through a burnt-bridge mechanism, during which nanosurface energy transfer (NSET) occurred between the fluorescent dye modified on hairpin DNA and the surface of gold nanoparticles (AuNPs). As a proof of concept, this stochastic DNA walker achieves prominent detection performance of HIV DNA in the range of 0.05-1.2 nM with a detection limit of 12.7 pM and satisfactory recovery in blood serum, showing high promise in biosensing applications with complicated media.

An electrochemical label-free DNA impedimetric sensor with AuNP-modified glass fiber/carbonaceous electrode for the detection of HIV-1 DNA.

In this study, a highly sensitive, electrochemical, and label-free DNA impedimetric sensor was developed using carbonized glass fiber–coal tar pitch (GF–CTP) electrodes supported with gold nanoparticles (AuNPs) for the detection of HIV-1 gene. Thiol-modified GF–CTP electrodes were prepared using amine crosslinking chemistry and AuNPs were self-assembled obtaining highly conductive nanoelectrodes, GF–CTP–ATP–Au. All steps of electrode modifications were characterized using electrochemical, spectroscopic, and microscopic methods. GF–CTP–ATP–Au electrode was then modified with a capture DNA probe (C-ssDNA) and optimized with a target DNA probe in terms of hybridization time and temperature between 30 and 180 min and 20–50 °C, respectively. Finally, the analytic performance of the developed ssDNA biosensor was evaluated using electrochemical impedance spectroscopy. The calibration of the sensor was obtained between 0.1 pM and 10 nM analyte working range. The limit of detection was calculated using signal to noise ratio of 3 (S/N = 3) as 13 fM. Moreover, interference results for two noncomplementary DNA probes were also tested to demonstrate non-specific ssDNA interactions. An electrochemical label-free DNA impedimetric sensor was successfully developed using a novel GF–CTP–ATP–Au electrode. This study suggests that highly sensitive DNA-based biosensors can be developed using relatively low-cost carbonaceous materials.

Three-cascade cycle amplification strategy for fluorescent detection of HIV-DNA in human blood with hybrid of pentaethylenehexamine-functionalized graphene quantum dot and NaGdF4:Yb,Er@NaGdF4

Poor water solubility and low efficiency of upconversion luminescence limit the applications of rare earth (RE)-doped upconversion nanoparticles in bioanalysis. The paper reports hybrid of pentaethylenehexamine functionalized graphene quantum dots and NaGdF4:Yb,Er@NaGdF4 via coordination of RE with nitrogen in the presence of polyvinylpyrrolidone. The resulting hybrid offers hexagonal nanostructure with particle size of 25 nm, good dispersibility and rich functional groups. Interestingly, the hybrid promotes the enhancement of upconversion luminescence that depends on the structure of graphene quantum dots. The hybrid was used as fluorescence probe for construction of three-cascade cycle amplification for detection of HIV-DNA. Target DNA interacts with the pre-hybridized duplex DNA to induce release of assistant strand DNA, triggering target DNA-induced recycle. The utilization of three-cascade cycle allows one target DNA to produce many tetramethylrhodamine-labeled DNA fragments. These are connected on the hybrid by complementary base pairs, promoting a significant upconversion fluorescence quenching by fluorescence resonance energy transfer, due to proximity of tetramethyl rhodamine and hybrid. The fluorescence signal decreases with increasing HIV-DNA concentration in the range of 1.0 × 10−17-1.0 × 10-12 M with the detection limit of 4.8 × 10-18 M. The proposed method provides advantage of sensitivity, specificity and stability and was successfully applied in detection of HIV-DNA in human blood.