PCR inhibitors and facilitators - Their role in forensic DNA analysis

Since its inception, DNA typing technology has been practiced as a robust tool in criminal investigations. Experts usually utilize STR profiles to identify and individualize the suspect. However, mtDNA and Y STR analyses are also considered in some sample-limiting conditions. Based on DNA profiles thus generated, forensic scientists often opine the results as Inclusion, exclusion, and inconclusive. Inclusion and exclusion were defined as concordant results; the inconclusive opinions create problems in conferring justice in a trial- since nothing concrete can be interpreted from the profile generated. The presence of inhibitor molecules in the sample is the primary factor behind these indefinite results. Recently, researchers have been emphasizing studying the sources of PCR inhibitors and their mechanism of inhibition. Furthermore, several mitigation strategies- to facilitate the DNA amplification reaction -have now found their place in the routine DNA typing assays with compromised biological samples. The present review paper attempts to provide a comprehensive review of PCR inhibitors, their source, mechanism of inhibition, and ways to mitigate their effect using PCR facilitators.

Application of Nanomaterials to Enhance Polymerase Chain Reaction

Polymerase Chain Reaction (PCR) is one of the most common technologies used to produce millions of copies of targeted nucleic acid in vitro and has become an indispensable technique in molecular biology. However, it suffers from low efficiency and specificity problems, false positive results, and so on. Although many conditions can be optimized to increase PCR yield, such as the magnesium ion concentration, the DNA polymerases, the number of cycles, and so on, they are not all-purpose and the optimization can be case dependent. Nano-sized materials offer a possible solution to improve both the quality and productivity of PCR. In the last two decades, nanoparticles (NPs) have attracted significant attention and gradually penetrated the field of life sciences because of their unique chemical and physical properties, such as their large surface area and small size effect, which have greatly promoted developments in life science and technology. Additionally, PCR technology assisted by NPs (NanoPCR) such as gold NPs (Au NPs), quantum dots (QDs), and carbon nanotubes (CNTs), etc., have been developed to significantly improve the specificity, efficiency, and sensitivity of PCR and to accelerate the PCR reaction process. This review discusses the roles of different types of NPs used to enhance PCR and summarizes their possible mechanisms.

Hyaluronic acid-modified polyamidoamine dendrimer G5-entrapped gold nanoparticles delivering METase gene inhibits gastric tumor growth via targeting CD44+ gastric cancer cells

BACKGROUND

Gastric cancer (GC) is the second most common leading cause of cancer-related death. Cancer stem cell (CSC) with the mark of CD44 played an important role in GC. rMETase was wildly exploited as chemotherapeutic option for GC. Polymers synthetic nanoparticle drug delivery systems have been commonly used for cancer therapy. With the decorating of Hyaluronic acid (HA), a receptor of CD44, nanoparticles exhibit with good biocompatibility and aqueous solubility.

METHODS

The characteristic of nanoparticles (NPs) was analyzed by TEM and DLS. The viability and proliferation of GC cells were examined by MTT assays. The levels of CD44, Cyt C, and c-caspase 3 were examined by Western blot. The level of ROS was measured by DCFH-DA assays. The morphology of tissues was detected using hematoxylin-eosin (H&E) stain. Nude mice xenograft models were used to evaluate the effect of HA-PAMAM-Au-METase on GC.

RESULTS

The transfection of rMETase carried by HA-G5 PAMAM-Au visibly inhibited the proliferation and tumorsphere formation of GC cells through obviously enhancing METase activity. Elevation of METase activity suppressed the proliferation of CD44(+) GC cells through down-regulating MET in cellular supernatant that resulted in the increase of Cyc C and ROS levels. The number of CD44(+) GC cells in nude mice injected with G5 PAMAM-Au-METase decorated by HA was markly declined resulting in the inhibition of tumor growth.

CONCLUSION

HA-G5 PAMAM-Au-METase significantly suppressed tumor growth of GC by targeted damaging the mitochondrial function of CD44(+) gastric CSCs.

Development of gold nanoparticles biosensor for ultrasensitive diagnosis of foot and mouth disease virus

Background

Nano-PCR is a recent tool that is used in viral diseases diagnosis. The technique depends on the fundamental effects of gold nanoparticles (AuNPs) and is considered a very effective and sensitive tool in the diagnosis of different diseases including viral diseases. Although several techniques are currently available to diagnose foot and mouth disease virus (FMDV), a highly sensitive, highly specific technique is needed for specific diagnosis of the disease. In the present work, a novel AuNPs biosensor has been designed using thiol-linked oligonucleotides that recognize the conserved 3D gene of FMDV.

Results

The AuNPs-FMDV biosensor specifically recognizes RNA standards of FMDV, but not that of swine vesicular disease virus (SVDV) isolates. The analytical sensitivity of the AuNPs-FMDV biosensor was 10 copy number RNA standards in RT-PCR and 1 copy number RNA standard in real-time rRT-PCR with a 94.5% efficiency, 0.989 R², a − 3.544 slope and 100% specificity (no cross-reactivity with SVDV). These findings were confirmed by the specific and sensitive recognition of 31 Egyptian FMDV clinical isolates that represents the three FMDV serotypes (O, A, and SAT2).

Conclusions

The AuNPs-FMDV biosensor presents in this study demonstrates a superior analytical and clinical performance for FMDV diagnosis. In addition, this biosensor has a simple workflow and accelerates epidemiological surveillance, hence, it is qualified as an efficient FMDV diagnosis tool for quarantine stations and farms particularly in FMDV endemic areas.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0374-x) contains supplementary material, which is available to authorized users.

Effect of antifouling dendrimers and Au DENPs on the enhancement of PCR amplification

The polymerase chain reaction (PCR) has been considered as one of the most fundamental techniques to amplify and analyze specific DNA fragments in the field of molecular biology and clinical medicine. Recently, a variety of nanoparticles (NPs) have been regarded as a novel method to enhance both the quality and yield of PCR technique. Herein, we report the use of generation 5 (G5) poly(amidoamine) (PAMAM) dendrimers and dendrimer-entrapped gold nanoparticles (Au DENPs) modified with polyethylene glycol (PEG) moieties and (or) acetyl groups as a novel class of enhancers to improve the PCR amplification. We set up the nonspecific PCR and two-round PCR as model systems to investigate mechanisms of enhanced PCR. Our results show that dendrimer-based derivatives seem to enhance the PCR specificity. It is worth noting that the modification of antifouling PEG significantly lowered the optimization capability of the corresponding dendrimers, although this inhibition effect can be remarkably compromised by the entrapment of Au NPs. Furthermore, we found that in the presence of Au NPs, the thermal conductivity induced by Au NPs could play the dominant role in the PCR optimization, whereas in the absence of Au NPs, the electrostatic interaction of the dendrimers with PCR components may be the major factor affecting the PCR system. Our results also showed that the optimal concentrations of the materials in the two test systems were very close, which indicates that the developed dendrimer derivatives with good thermal stability may be the efficient PCR additives for enhancing different PCR systems.

Enhancing the specificity of polymerase chain reaction by graphene oxide through surface modification: zwitterionic polymer is superior to other polymers with different charges

Graphene oxides (GOs) with different surface characteristics, such as size, reduction degree and charge, are prepared, and their effects on the specificity of polymerase chain reaction (PCR) are investigated. In this study, we demonstrate that GO with a large size and high reduction degree is superior to small and nonreduced GO in enhancing the specificity of PCR. Negatively charged polyacrylic acid (PAA), positively charged polyacrylamide (PAM), neutral polyethylene glycol (PEG) and zwitterionic polymer poly(sulfobetaine) (pSB) are used to modify GO. The PCR specificity-enhancing ability increases in the following order: GO-PAA < GO-PAM < GO-PEG < GO-pSB. Thus, zwitterionic polymer-modified GO is superior to other GO derivatives with different charges in enhancing the specificity of PCR. GO derivatives are also successfully used to enhance the specificity of PCR for the amplification of human mitochondrial DNA using blood genomic DNA as template. Molecular dynamics simulations and molecular docking are performed to elucidate the interaction between the polymers and Pfu DNA polymerase. Our data demonstrate that the size, reduction degree and surface charge of GO affect the specificity of PCR. Based on our results, zwitterionic polymer-modified GO may be used as an efficient additive for enhancing the specificity of PCR.

Mechanistic Studies of Enhanced PCR Using PEGylated PEI-Entrapped Gold Nanoparticles

The polymerase chain reaction (PCR) is considered an excellent technique and is widely used in both molecular biology research and various clinical applications. However, the presence of byproducts and low output are limitations generally associated with this technique. Recently, the use of nanoparticles (NPs) has been shown to be very effective at enhancing PCR. Although mechanisms underlying this process have been suggested, most of them are mainly based on PCR results under certain situations without abundant systematic experimental strategy. In order to overcome these challenges, we synthesized a series of polyethylene glycol (PEG)-modified polyethylenimine (PEI)-entrapped gold nanoparticles (PEG-Au PENPs), each having different gold contents. The role of the synthesized NPs in improving the PCR technique was then systematically evaluated using the error-prone two-round PCR and GC-rich PCR (74% GC content). Our results suggest a possible mechanism of PCR enhancement. In the error-prone two-round PCR system, the improvement of the specificity and efficiency of the technique using the PEG-Au PENPs mainly depends on surface-charge-mediated electrostatic interactions. In the GC-rich PCR system, thermal conduction may be the dominant factor. These important findings offer a breakthrough in understanding the mechanisms involved in improving PCR amplification, as well as in the application of nanomaterials in different fields, particularly in biology and medicine.

Metal nanoparticle assisted polymerase chain reaction for strain typing of Salmonella Typhi

Salmonella enterica serotype Typhi (S. Typhi) is the causative agent of typhoid fever and remains a major health threat in most of the developing countries. The prompt diagnosis of typhoid directly from the patient's blood requires high level of sensitivity and specificity. Some of us were the first to report PCR based diagnosis of typhoid. This approach has since then been reported by many scientists using different genomic targets. Since the number of bacteria circulating in the blood of a patient can be as low as 0.3 cfu ml(-1), there is always a room for improvement in diagnostic PCR. In the present study, the role of different types of nanoparticles was investigated to improve the existing PCR based methods for diagnosis and strain typing of S. Typhi (targeting Variable Number of Tandem Repeats [VNTR]) by using optimized PCR systems. Three different types of nanoparticles were used i.e., citrate stabilized gold nanoparticles, rhamnolipid stabilized gold and silver nanoparticles, and magnetic iron oxide nanoparticles. The non-specific amplification was significantly reduced in VNTR typing when gold and silver nanoparticles were used in an appropriate concentration. More importantly, the addition of nanoparticles decreased the non-specificity to a significant level in the case of multiplex PCR thus further validating the reliability of PCR for the diagnosis of typhoid.

Nanosized Fe3O4 an efficient PCR yield enhancer-Comparative study with Au, Ag nanoparticles

Nanomaterials-assisted PCR is a promising field of nanobiotechnology that amalgamates nanomaterials into the conventional PCR system to achieve better amplification of desired product. With literature documenting the variable effects of these nanomaterials on the PCR yield and amplification; it was thought worthwhile to compare the PCR enhancing efficiency of three transition metal nanoparticles in form of stable colloidal suspensions at varying concentrations.The nanoparticles(NPs) of silver, gold and magnetite were chemically synthesized by reducing their respective salts and characterized using UV-vis spectroscopy. Their morphology was assessed using nanoparticle tracking system and AFM. The effect of these nanofluids on amplification of 800 bp prokaryotic DNA template with 30% GC content was studied using conventional thermal cycler. The reaction kinetics for all the three nanofluids yielded a Gaussian curve of amplification with varying concentrations. The ammonium salt of oleic acid coated magnetite (Fe3O4) nanoparticles at a concentration of 0.72 × 10(-2)nM and average size of 33 nm demonstrated highest amplification efficiency of 190% as compared to the citrate stabilized AgNP-25 nm (45%) and AuNP-15.19 nm (134%) using a conventional PCR system. The major reasons that allow Fe3O4 NPs outperform the other 2 transition metal NP's seem to be attributed to its heat conduction property as well as effective adsorption of PCR components onto the ammonium salt of oleic acid coated magnetite nanofluids. The data from our study offers valuable information for the application of ferrofluids as economically, efficient and effective alternative for nanomaterial-assisted PCR yield enhancers.

Nanoparticles Affect PCR Primarily via Surface Interactions with PCR Components: Using Amino-Modified Silica-Coated Magnetic Nanoparticles as a Main Model

Nanomaterials have been widely reported to affect the polymerase chain reaction (PCR). However, many studies in which these effects were observed were not comprehensive, and many of the proposed mechanisms have been primarily speculative. In this work, we used amino-modified silica-coated magnetic nanoparticles (ASMNPs, which can be collected very easily using an external magnetic field) as a model and compared them with gold nanoparticles (AuNPs, which have been studied extensively) to reveal the mechanisms by which nanoparticles affect PCR. We found that nanoparticles affect PCR primarily by binding to PCR components: (1) inhibition, (2) specifity, and (3) efficiency and yield of PCR are impacted. (1) Excess nanomaterials inhibit PCR by adsorbing to DNA polymerase, Mg(2+), oligonucleotide primers, or DNA templates. Nanoparticle surface-active groups are particularly important to this effect. (2, a) Nanomaterials do not inhibit nonspecific amplification products caused by false priming as previously surmised. It was shown that relatively low concentrations of nanoparticles inhibited the amplification of long amplicons, and increasing the amount of nanoparticles inhibited the amplification of short amplicons. This concentration phenomenon appears to be the result of the formation of "joints" upon the adsorption of ASMNPs to DNA templates. (b) Nanomaterials are able to inhibit nonspecific amplification products due to incomplete amplification by preferably adsorbing single-stranded incomplete amplification products. (3) Some types of nanomaterials, such as AuNPs, enhance the efficiency and yield of PCR because these types of nanoparticles can adsorb to single-stranded DNA more strongly than to double-stranded DNA. This behavior assists in the rapid and thorough denaturation of double-stranded DNA templates. Therefore, the interaction between the surface of nanoparticles and PCR components is sufficient to explain most of the effects of nanoparticles on PCR.

RGD peptide-modified dendrimer-entrapped gold nanoparticles enable highly efficient and specific gene delivery to stem cells

We report the use of arginine-glycine-aspartic (Arg-Gly-Asp, RGD) peptide-modified dendrimer-entrapped gold nanoparticles (Au DENPs) for highly efficient and specific gene delivery to stem cells. In this study, generation 5 poly(amidoamine) dendrimers modified with RGD via a poly(ethylene glycol) (PEG) spacer and with PEG monomethyl ether were used as templates to entrap gold nanoparticles (AuNPs). The native and the RGD-modified PEGylated dendrimers and the respective well characterized Au DENPs were used as vectors to transfect human mesenchymal stem cells (hMSCs) with plasmid DNA (pDNA) carrying both the enhanced green fluorescent protein and the luciferase (pEGFPLuc) reporter genes, as well as pDNA encoding the human bone morphogenetic protein-2 (hBMP-2) gene. We show that all vectors are capable of transfecting the hMSCs with both pDNAs. Gene transfection using pEGFPLuc was demonstrated by quantitative Luc activity assay and qualitative evaluation by fluorescence microscopy. For the transfection with hBMP-2, the gene delivery efficiency was evaluated by monitoring the hBMP-2 concentration and the level of osteogenic differentiation of the hMSCs via alkaline phosphatase activity, osteocalcin secretion, calcium deposition, and von Kossa staining assays. Our results reveal that the stem cell gene delivery efficiency is largely dependent on the composition and the surface functionality of the dendrimer-based vectors. The coexistence of RGD and AuNPs rendered the designed dendrimeric vector with specific stem cell binding ability likely via binding of integrin receptor on the cell surface and improved three-dimensional conformation of dendrimers, which is beneficial for highly efficient and specific stem cell gene delivery applications.

Dendrimer–nanoparticle conjugates in nanomedicine

Nanomedicine can take advantage of the recent developments in nanobiotechnology research areas for the creation of platforms with superior drug carrier capabilities, selective responsiveness to the environment, unique contrast enhancement profiles and improved accumulation at the disease site. Colloidal inorganic nanoparticles (NPs) have been attracting considerable interest in biomedicine, from drug and gene delivery to imaging, sensing and diagnostics. It is essential to modify the NPs surface to have enhanced biocompatibility and reach multifunctional systems for the in vitro and in vivo applications, especially in delivering drugs locally and recognizing overexpressed biomolecules. This paper describes the rational design for dendrimer–nanoparticle conjugates elaboration and reviews their state-of-the-art uses as efficient nanomedicine tools.

Bovine thrombin enhances the efficiency and specificity of polymerase chain reaction

The polymerase chain reaction (PCR) has become one of the central techniques in molecular biology since its invention. However, PCR can be fraught with difficulties in various situations, and it is desirable to find novel PCR enhancers suitable for universal applications. Here we show that bovine thrombin (BT), a well-known coagulation protein, is exceptionally effective at preventing the formation of primer dimers and enhancing the formation of the desired PCR products. The PCR enhancement effects of BT were demonstrated by testing various types of samples, including low-copy synthetic single-stranded DNAs (ssDNAs), synthetic ssDNA pools, human genomic DNA, and hepatitis B virus genomic DNA. In addition, BT was also able to effectively relieve PCR inhibition by nanomaterial inhibitors such as gold nanoparticles (AuNPs) and graphene oxide (GO). Compared with BSA, one of the most popular PCR enhancers, BT was more effective and required concentrations 18-178 times less than that of BSA to achieve a similar level of PCR enhancement.

A hot start alternative for high-fidelity DNA polymerase amplification mediated by quantum dots

Quantum dots (QDs) are of great interest due to their unique chemical and physical properties. Recently, a hot start (HS) polymerase chain reaction (PCR) amplification performance based on QDs with a high-fidelity Pfu DNA polymerase has been reported. However, whether QDs can trigger HS effects with other high-fidelity or conventional DNA polymerases is yet to be understood. In the present study, we studied the QD-triggered HS effects with four high-fidelity and three conventional DNA polymerases, and the HS effect comparisons among them were also made. It was found that QDs could trigger a distinct HS PCR amplification performance with all the four tested high-fidelity DNA polymerases, and specific target DNA could be well amplified even if the PCR mixture was pre-incubated for 2 h at 50°C. On the contrary, the HS effects were not prominent with all the three conventional Taq DNA polymerases. Specifically, the fidelity of Pfu is not sacrificed in the presence of QDs, even after a 1 h pre-incubation at 50°C before PCR. Furthermore, the electrophoresis results preliminarily demonstrated that QDs prefer to adsorb high-fidelity polymerases rather than conventional ones, which might result in the QD-triggered HS effects on PCR performance by using high-fidelity DNA polymerases.

Effect of surface charge of PDDA-protected gold nanoparticles on the specificity and efficiency of DNA polymerase chain reaction

The polymerase chain reaction (PCR) has become an indispensable technique in molecular biology, however, it suffers from low efficiency and specificity problems. Developing suitable additives to effectively avoid nonspecific PCR reactions and explore the mechanism for PCR enhancing is a significant challenge. In this paper, we report three different modified gold nanoparticles (AuNPs) with different surface charge polarities and poly (diallyl dimethylammonium) chloride (PDDA) for use as novel PCR enhancers to improve the efficiency and specificity. These AuNPs included the positively charged PDDA protected AuNPs (PDDA-AuNPs), the neutral PDDA-AuNPs modified with excess chloride ion (PDDA.C-AuNPs), and the negatively charged sodium citrate (Na(3)Ct) protected AuNPs (Na(3)Ct-AuNPs). Our data clearly suggests that the positively charged PDDA-AuNPs with an optimum concentration as low as 1.54 pM could significantly enhance the specificity and efficiency of PCR, however, the optimum concentration of the negatively charged Na(3)Ct-AuNPs (2.02 nM) was more than 3 orders of magnitude higher than that of positively charged PDDA-AuNPs. The PCR specificity and efficiency are also improved by the neutral PDDA.C-AuNPs with an optimum concentration, much more than that of the PDDA-AuNPs. This suggests that there should be an electrostatic interaction between the positively charged PDDA-AuNPs and the negatively charged PCR components, and the surface charge polarities of PDDA-AuNPs may play an important role in improving the PCR specificity and efficiency.

Employment of nanomaterials in polymerase chain reaction: insight into the impacts and putative operating mechanisms of nano-additives in PCR

The latest developments in the field of nanomaterial-assisted PCR are evaluated with a focus on putative operating mechanisms.

Enhanced PCR amplification of GC-rich DNA templates by gold nanoparticles

Gold nanoparticles (AuNPs) have been reported to facilitate double-stranded DNA dissociation and improve performance of several PCR systems. Here we investigated AuNPs' effect on GC-rich DNA amplification. We found that AuNPs could enhance PCR amplification of the GNAS1 promoter region (∼84% GC) mediated by Pfu or Taq DNA polymerase. However, under optimal concentrations of AuNPs, higher amounts of Taq were required. Furthermore, the GC-rich FMR1 (80.4% GC) gene of Homo sapiens as well as exoT (67.3% GC), exsE (71% GC) and pqqF genes (74% GC) of Pseudomonas aeruginosa were also efficiently amplified. AuNPs can become an effective additive in GC-rich PCR and facilitate analysis of challenging genomic sequence in basic and clinical research.

Dendrimer-entrapped gold nanoparticles modified with folic acid for targeted gene delivery applications

We report a new use of dendrimer-entrapped gold nanoparticles (Au DENPs) modified with folic acid (FA) as a non-viral vector for targeted gene delivery applications. In this study, amine-terminated generation 5 poly(amidoamine) dendrimers modified with FA via covalent conjugation were used as templates to synthesize gold nanoparticles with an Au salt/dendrimer molar ratio of 25 : 1. The synthesized FA-modified Au DENPs (Au DENPs-FA) were used as a non-viral vector for the delivery of plasmid DNA (pDNA) into a model cancer cell line (HeLa cells) overexpressing high-affinity FA receptors (FAR). The DNA compaction ability of the formed Au DENPs-FA was systematically characterized using a gel retardation assay, zeta potential, and dynamic light scattering. We show that similar to the Au DENPs vector without FA, the Au DENPs-FA vector was able to compact the pDNA encoding enhanced green fluorescent protein (EGFP) at an N/P ratio of 0.5. Transfection results show that the Au DENPs-FA vector enables much higher luciferase and EGFP gene expression in HeLa cells overexpressing FAR than the Au DENPs without FA, demonstrating the role played by FA-mediated targeting for enhanced gene transfection in target cells. With a lower cytotoxicity than that of the Au DENPs without FA proven by a cell viability assay, the developed FA-modified Au DENPs may be used as a promising non-viral vector for safe and targeted gene therapy applications.

Polycations-functionalized water-soluble gold nanoclusters: a potential platform for simultaneous enhanced gene delivery and cell imaging

Noble metal nanoclusters have emerged as a fascinating area of widespread interest in nanomaterials. Herein, we report the synthesis of the PEI-templated gold nanoclusters (PEI-AuNCs) as an efficient carrier for gene delivery. The PEI-AuNCs integrate the advantages of PEI and AuNCs: the presence of AuNCs can effectively decrease the cytotoxicity of PEI, making it possible to apply them in biological systems, while the cationic polymer layer PEI with positive charges is essential for enhanced gene transfection efficiency. In addition, with excellent photoluminescent properties, the AuNCs also endow our system with the versatility of fluorescent imaging, indicating a great potential as an ideal fluorescent probe to track the transfection behavior. Our studies provide strong evidence that the PEI-AuNCs can be utilized as efficient gene delivery agents.

Genetic analysis with nanoPCR

Polymerase chain reaction (PCR) has become a standard and important molecular biological technique with numerous applications in genetic analysis, forensics and in vitro diagnostics. Since its invention in the 1980s, there has been dramatic performance improvement arising from long-lasting efforts to optimize amplification conditions in both academic studies and commercial applications. More recently, a range of nanometer-sized materials including metal nanoparticles, semiconductor quantum dots, carbon nanomaterials and polymer nanoparticles, have shown unique effects in tuning amplification processes of PCR. It is proposed that these artificial nanomaterials mimic protein components in the natural DNA replication machinery in vivo. These so-called nanomaterials-assisted PCR (nanoPCR) strategies shed new light on powerful PCR with unprecedented sensitivity, selectivity and extension rate. In this review, we aim to summarize recent progress in this direction and discuss possible mechanisms for such performance improvement and potential applications in genetic analysis (particularly gene typing and haplotyping) and diagnostics.

Enhancing the specificity and efficiency of polymerase chain reaction using polyethyleneimine-based derivatives and hybrid nanocomposites

There is a general necessity to improve the specificity and efficiency of the polymerase chain reaction (PCR), and exploring the PCR-enhancing mechanism still remains a great challenge. In this paper we report the use of branched polyethyleneimine (PEI)-based derivatives and hybrid nanocomposites as a novel class of enhancers to improve the specificity and efficiency of a nonspecific PCR system. We show that the surface-charge polarity of PEI and PEI derivatives plays a major role in their effectiveness to enhance the PCR. Positively charged amine-terminated pristine PEI, partially (50%) acetylated PEI (PEI-Ac(50)), and completely acetylated PEI (PEI-Ac) are able to improve PCR efficiency and specificity with an optimum concentration order of PEI < PEI-Ac(50) < PEI-Ac, whereas negatively charged carboxyl-terminated PEI (PEI-SAH; SAH denotes succinamic acid groups) and neutralized PEI modified with both polyethylene glycol (PEG) and acetyl (Ac) groups (PEI-PEG-Ac) are unable to improve PCR specificity and efficiency even at concentrations three orders of magnitude higher than that of PEI. Our data clearly suggests that the PCR-enhancing effect is primarily based on the interaction between the PCR components and the PEI derivatives, where electrostatic interaction plays a major role in concentrating the PCR components locally on the backbones of the branched PEI. In addition, multiwalled carbon nanotubes modified with PEI and PEI-stabilized gold nanoparticles are also able to improve the PCR specificity and efficiency with an optimum PEI concentration less than that of the PEI alone, indicating that the inorganic component of the nanocomposites may help improve the interaction between PEI and the PCR components. The developed PEI-based derivatives or nanocomposites may be used as efficient additives to enhance other PCR systems for different biomedical applications.

Gene delivery using dendrimer-entrapped gold nanoparticles as nonviral vectors

Development of highly efficient nonviral gene delivery vectors still remains a great challenge. In this study, we report a new gene delivery vector based on dendrimer-entrapped gold nanoparticles (Au DENPs) with significantly higher gene transfection efficiency than that of dendrimers without AuNPs entrapped. Amine-terminated generation 5 poly(amidoamine) (PAMAM) dendrimers (G5.NH(2)) were utilized as templates to synthesize AuNPs with different Au atom/dendrimer molar ratios (25:1, 50:1, 75:1, and 100:1, respectively). The formed Au DENPs were used to complex two different pDNAs encoding luciferase (Luc) and enhanced green fluorescent protein (EGFP), respectively for gene transfection studies. The Au DENPs/pDNA polyplexes with different N/P ratios and compositions of Au DENPs were characterized by gel retardation assay, light scattering, zeta potential measurements, and atomic force microscopic imaging. We show that the Au DENPs can effectively compact the pDNA, allowing for highly efficient gene transfection into the selected cell lines as demonstrated by both Luc assay and fluorescence microscopic imaging of the EGFP expression. The transfection efficiency of Au DENPs with Au atom/dendrimer molar ratio of 25:1 was at least 100 times higher than that of G5.NH(2) dendrimers without AuNPs entrapped at the N/P ratio of 2.5:1. The higher gene transfection efficiency of Au DENPs is primarily due to the fact that the entrapment of AuNPs helps preserve the 3-dimensional spherical morphology of dendrimers, allowing for more efficient interaction between dendrimers and DNA. With the less cytotoxicity than that of G5.NH(2) dendrimers demonstrated by thiazoyl blue tetrazolium bromide assay and higher gene transfection efficiency, it is expected that Au DENPs may be used as a new gene delivery vector for highly efficient transfection of different genes for various biomedical applications.