Ultrasensitive DNA detection using oligonucleotide-silver nanoparticle conjugates

Nanoparticle assembly for sensitive DNA detection using SERRS

SERRS (surface-enhanced resonance Raman scattering) is a vibrational technique, whereby a relatively weak Raman scattering effect is enhanced through the use of a visible chromophore and a roughened metal surface. The direct analysis of DNA by SERRS requires the modification of a nucleic acid sequence to incorporate a chromophore, and adsorption of the modified sequence on to a roughened metal surface. Aggregated metallic nanoparticles are commonly used in the analysis of dye-labelled DNA by SERRS, allowing for detection levels that rival those gained from standard fluorescence-based techniques. In the present paper, we report on how SERRS can be exploited for the analysis of clinically relevant DNA samples. We also report on the ability of nanoparticles to aggregate as the result of a biologically significant event, as opposed to the use of an external charge-modifying agent. The self-assembly of metallic nanoparticles is shown to be a promising new technique in the move towards extremely sensitive methods of DNA analysis by SERRS.

Aptamer-nanoparticle assembly for logic-based detection

In this work, gold nanoparticles perform Boolean logic operations in response to two proangiogenic targets important in cancer diagnosis and treatment: PDGF and VEGF. In the absence of protein target, gold nanoparticles are initially dispersed as a red solution; the addition of target proteins causes nanoparticle aggregation, turning the solution blue, as well as the release of dye-labeled aptamer probes, which causes an increase in fluorescence. These outputs constitute an AND or OR gate for simultaneous protein detection. We believe this logic-gate-based detection system will become the basis for novel rapid, cheap, and reliable sensors for diagnostic applications.

Rapid transformation from spherical nanoparticles, nanorods, cubes, or bipyramids to triangular prisms of silver with PVP, citrate, and H2O2

Rapid sphere-to-prism (STP) transformation of silver was studied in aqueous AgNO(3)/NaBH(4)/polyvinylpyrrolidone (PVP)/trisodium citrate (Na(3)CA)/H(2)O(2) solutions by monitoring time-dependent surface plasmon resonance (SPR) bands in the UV-vis region, by examining transmission electron microscopic (TEM) images, and by analyzing emitted gases during fast reaction. Roles of PVP, Na(3)CA, and H(2)O(2) were studied without addition of a reagent, with different timing of each reagent's addition, and with addition of H(2)O(2) to mixtures of spheres and prisms. Results show that prisms can be prepared without addition of PVP, although it is useful to synthesize smaller monodispersed prisms. A new important role of citrate found in this study, besides a known role as a protecting agent of {111} facets of plates, is an assistive agent for shape-selective oxidative etching of Ag nanoparticles by H(2)O(2). The covering of Ag nanoparticles with carboxylate groups is necessary to initiate rapid STP transformation by premixing citrate before H(2)O(2) addition. Based on our data, rapid prism formation starts from the consumption of spherical Ag particles because of shape-selective oxidative etching by H(2)O(2). Oxidative etching of spherical particles by H(2)O(2) is faster than that of prisms. Therefore, spherical particles are selectively etched and dissolved, leaving only seeds of prisms to grow into triangular prisms. When pentagonal Ag nanorods and a mixture of cubes and bipyramids were used as sources of prisms, rod-to-prism (RTP), cube-to-prism (CTP), and bipyramid-to-prism (BTP) transformations were observed in Ag nanocrystals/NaBH(4)/PVP/Na(3)CA/H(2)O(2) solutions. Shape-selective oxidative etching of rods was confirmed using flag-type Ag nanostructures consisting of a triangular plate and a side rod. These data provide useful information for the size-controlled synthesis of triangular Ag prisms, from various Ag nanostructures and using a chemical reduction method, having surface plasmon resonance (SPR) bands at a desired wavelength.

One-step conjugation chemistry of DNA with highly scattered silver nanoparticles for sandwich detection of DNA

DNA-silver nanoparticle (AgNP) conjugates were facilely prepared through a one-step method, and then used for the quantitative detection of HIV DNA with a sandwich strategy based on their strong plasmon resonance scattering signals.

Synthesis of different-sized silver nanoparticles by simply varying reaction conditions with leaf extracts of Bauhinia variegata L

Green synthesis of nanoparticles is one of the crucial requirements in today's climate change scenario all over the world. In view of this, leaf extract (LE) of Bauhinia variegata L. possessing strong antidiabetic and antibacterial properties has been used to synthesise silver nanoparticles (SNP) in a controlled manner. Various-sized SNP (20-120 nm) were synthesised by varying incubation temperature, silver nitrate and LE concentrations. The rate of SNP synthesis and their size increased with increase in AgNO(3) concentration up to 4 mM. With increase in LE concentration, size and aggregation of SNP was increased. The size and aggregation of SNP were also increased at temperatures above and below 40°C. This has suggested that size and dispersion of SNP can be controlled by varying reaction components and conditions. Polarity-based fractionation of B. variegata LE has suggested that only water-soluble fraction is responsible for SNP synthesis. Fourier transform infrared spectroscopy analysis revealed the attachment of polyphenolic and carbohydrate moieties to SNP. The synthesised SNPs were found stable in double distilled water, BSA and phosphate buffer (pH 7.4). On the contrary, incubation of SNP with NaCl induced aggregation. This suggests the safe use of SNP for various in vivo applications.

Fluorescence enhancement of silver nanoparticle hybrid probes and ultrasensitive detection of IgE

An ultrasensitive protein assay method was developed based on silver nanoparticle (AgNP) hybrid probes and metal-enhanced fluorescence. Two aptamer based silver nanoparticles, Aptamer/Oligomer-A/Cy3-modified AgNPs (Tag-A) and Aptamer/Oligomer-B/Cy3-modified AgNPs (Tag-B) were hybridized to form a silver nanoparticle aggregate that produced a red shift and broadening of the Localized Surface Plasmon Resonance (LSPR) peak. The enhanced fluorescence resulted from the increased content of Cy3 molecules and their emission resonance coupled to the broadened localized surface plasmon (LSP) of AgNP aggregate. The separation distance between Cy3 and AgNPs was 8 nm which was the most optimal for metal enhanced fluorescence and the separation distance between adjacent AgNPs was about 16 nm and this was controlled by the lengths of oligomer-A and oligomer-B. The protein array was prepared by covalently immobilizing capture antibodies on aldehyde-coated slide. After addition of protein IgE sample, two kinds of aptamer-modified AgNPs (Tag-A and Tag-B) were employed to specifically recognize IgE and form the AgNP aggregate on the arrays based on their hybridization. The detection property of the aptamer-modified AgNP aggregate was compared to two other modified aptamer-based probes, aptamer-modified Cy3 and Tag-A. The modified AgNP hybrid probe (Tag-A and Tag-B) showed remarkable superiority in both sensitivity and detection limit due to the formed AgNP aggregate. The new hybrid probe also produced a wider linear range from 0.49 to 1000 ng/mL with the detection limit reduced to 40 pg/mL (211 fM). The presented method showed that the newly designed strategy of combining aptamer-based nanomaterials to form aggregates results in a highly sensitive optical detection method based on localized surface plasmon.

Polymeric sequence probe for single DNA detection

A polynucleotide probe, polymeric sequence probe (PSP), was developed for single molecular detections. PSP is a single-stranded DNA molecule with ~2000 tandem repeat target-binding sequences and label-binding sequences. A single PSP can bind to multiple fluorescent complementary oligos to generate a strong fluorescence signal. Single target molecules bound to PSPs can be clearly visualized by a conventional fluorescence microscope. An ultrasensitive PSP-based assay for Mycobacterium tuberculosis was demonstrated.

Synthesis of Ag(2) S-Ag nanoprisms and their use as DNA hybridization probes

A simple synthetic route to prepare Ag(2) S-Ag nanoprisms consists of the facile addition of Na(2) S to a solution of triangular Ag nanoprisms. The resulting Ag(2) S-Ag nanoparticles are more stable in solution than the original Ag nanoprisms, and two surface plasmon resonance (SPR) bands of the original Ag nanoprisms still remain. In addition, the SPR bands of the Ag(2) S-Ag nanoprisms are tunable over a wide range. The Ag(2) S-Ag nanoprisms can be directly bioconjugated via well-established stable Ag(2) S surface chemistry with readily available sulfur coupling agents. The nanoprisms are used in the hybridization of functionalized oligonucleotides, and show promise as probes for future biosensing applications.

Combining functionalised nanoparticles and SERS for the detection of DNA relating to disease

DNA functionalised nanoparticle probes offer new opportunities in analyte detection. Ultrasensitive, molecularly specific targeting of analytes is possible through the use of metallic nanoparticles and their ability to generate a surface enhanced Raman scattering (SERS) response. This is leading to a new range of diagnostic clinical probes based on SERS detection. Our approaches have shown how such probes can detect specific DNA sequences by using a biomolecular recognition event to 'turn on' a SERS response through a controlled assembly process of the DNA functionalised nanoparticles. Further, we have prepared DNA aptamer functionalised SERS probes and demonstrated how introduction of a protein target can change the aggregation state of the nanoparticles in a dose-dependant manner. These approaches are being used as methods to detect biomolecules that indicate a specific disease being present with a view to improving disease management.

Simultaneous detection of multiple biomarkers with over three orders of concentration difference using phase change nanoparticles

A big challenge for multiplexed detection of cancer biomarkers is that biomarker concentrations in body fluid differs several orders of magnitude. Existing techniques are not suitable to detect low- and high-concentration biomarkers (protein and DNA) at the same time, and liquid chromatography or electrophoresis is used to separate or purify target biomarkers before analysis. This paper describes a new broad-range biomarker assay using solid to liquid phase change nanoparticles, where a panel of metallic nanoparticles (i.e., metals and eutectic alloys) are modified with a panel of ligands to establish a one-to-one correspondence and attached onto ligand-modified substrates by forming sandwiched complexes. The melting peak and fusion enthalpy of phase change nanoparticles during thermal analysis reflect the type and concentration of biomarkers, respectively. The thermal readout condition can be adjusted in such a way that multiple biomarkers with concentration difference over 3 orders of magnitude have been simultaneously detected under the same condition.

Dual-signal fenamithion probe by combining fluorescence with colorimetry based on Rhodamine B modified silver nanoparticles

A versatile yet simple strategy for the fabrication of a highly selective and sensitive fenamithion probe based on Rhodamine B (RB) modified silver nanoparticles (RB-Ag NPs) was developed. The advantage of our system over classical assays is that it combined fluorescence with colorimetry which can realize the prompt on-site and real-time detection of fenamithion with high sensitivity (0.1 nM) in aqueous solution. Moreover, the detection system presents excellent anti-disturbance ability when exposed to a series of interfering ionic/pesticides mixtures and can be applied to the determination of fenamithion in real vegetables and different water samples with the limit of detection (LOD) as low as 10 nM (0.0026 mg L(-1)), which is in accord with the maximum contamination level of 0.001∼0.25 mg L(-1) for organophosphorus pesticides as defined by the U.S. Environmental Protection Agency (EPA). Advantage is taken of the fact that RB would be displaced from the surface of the Ag NPs because of the stronger coordination ability of Ag NPs with fenamithion, an amino-containing organophosphorus pesticide, accompanying the clustered Ag NPs (9 nm) dissipating into smaller individual particles (7 nm). Based on this phenomenon, a novel analyte-induced etching mechanism was proposed.

Colorimetric chiral recognition of enantiomers using the nucleotide-capped silver nanoparticles

Chiral recognition is among the important and special modes of molecular recognition. It is highly desirable to develop a simple, rapid, sensitive, and high-throughput routine assay for chiral recognition. In this study, we demonstrate that nucleotide-capped Ag nanoparticles (AgNPs) can be used as an ultrahigh efficiency enantioseparation and detection platform for D- and L-cysteine. The aggregation of AgNPs is selectively induced by an enantiomer of cysteine, which allowed the rapid colorimetric enantiodiscrimination of cysteine without any prior derivatization and specific instruments and left an excess of the other enantiomer in the solution, thus resulting in enantioseparation. This is the first application of a nucleotide-capped AgNP-based biosensing platform for chiral recognition and opens new opportunities for design of more novel enantiosensing strategies and enantiospecific adsorbents and expansion of its application in different fields.

An electrochemical supersandwich assay for sensitive and selective DNA detection in complex matrices

In a traditional sandwich assay, a DNA target hybridizes to a single copy of the signal probe. Here we employ a modified signal probe containing a methylene blue (a redox moiety) label and a "sticky end." When a DNA target hybridizes this signal probe, the sticky end remains free to hybridize another target leading to the creation of a supersandwich structure containing multiple labels. This leads to large signal amplification upon monitoring by voltammetry.

A universal platform for sensitive and selective colorimetric DNA detection based on Exo III assisted signal amplification

Rapid growth of available sequence data has made the detection of nucleic acids critical to the development of modern life sciences. Many amplification methods based on gold nanoparticles and endonuclease for sensitive DNA detection have been developed. However, these approaches require specific target sequence for endonuclease recognition, which cannot be fulfilled in all systems. Replacing the restriction enzyme with a nuclease that does not require any specific recognition sequence may offer a universally adaptable system. Here we have developed a novel homogeneous, colorimetric DNA detection method, which consists of Exo III, a linker DNA, and two DNA-modified gold nanoparticles. This system is simple, low-cost, sensitive and selective. By coupling cyclic enzymatic cleavage and gold nanoparticle for signal amplification, our system provides a colorimetric detection limit of 15 pM, which is 3 orders of magnitude more sensitive than that of a general three-component sandwich assay format. Due to the intrinsic property of Exo III, our method shows excellent detection selectivity for single-base discrimination. More importantly, superior to other methods based on nicking and FokI endonuclease, our target sequence-independent platform is generally applicable for DNA sensing. This new approach could be widely applied to sensitive nucleic acids detection.

Recent advancements in optical DNA biosensors: exploiting the plasmonic effects of metal nanoparticles

The emerging field of plasmonics, the study of electromagnetic responses of metal nanostructures, has revealed many novel signal enhancing phenomena. As applied to the development of label-free optical DNA biosensors, it is now well established that plasmon-based surface enhanced spectroscopies on nanostructured metal surfaces or metal nanoparticles can markedly improve the sensitivity of optical biosensors, with some showing great promise for single molecule detection. In this review, we first summarize the basic concepts of plasmonics in metal nanostructures, as well as the characteristic optical phenomena to which plasmons give rise. We will then describe recent advances in optical DNA biosensing systems enabled by metal nanoparticle-derived plasmonic effects, including the use of surface enhanced Raman scattering (SERS), colorimetric methods, "scanometric" processes, and metal-enhanced fluorescence (MEF).

The effect of humic acids on the cytotoxicity of silver nanoparticles to a natural aquatic bacterial assemblage

The effect of a terrestrial humic acid (HA) and a river HA on the cytotoxicity of silver nanoparticles (AgNPs) to natural aquatic bacterial assemblages (0 μM, 2.5 μM and 5 μM) was measured with spread plate counting. The effect of HA (20 and 40 ppm) on the cytotoxicity of AgNPs ranging in size between 15 and 25 nm was tested in the presence and in the absence of natural sunlight. The experiment was a full factorial, completely randomized design and the results were analyzed using the General Linear Model in SAS. LSMEANS was used to separate the means or combinations of means. Significant main effects of all independent variables, plus interaction effects in all cases except HA/LI and HA/AgNPs/LI were observed. The toxicity of AgNPs to natural aquatic bacterial assemblages appears to be concentration dependent for concentrations between 0 μM and 5 μM. The data indicate that the light exposure inhibited viability more than the darkness exposure. The HA treatment groups in the presence of light showed greater reduced viability count compared to darkness exposure groups. The inhibition of bacterial viability counts by AgNPs exposure was less in the light treatment groups containing a terrestrial HA compared to that with a river HA. Difference in the extent of reactive oxygen species formation and adsorption/binding of AgNPs was speculated to account for the observed phenomenon.

Chemical redox-regulated mesoporous silica-coated gold nanorods for colorimetric probing of Hg2+ and S2-

The past a few years have witnessed the wide use of metallic nanoparticles as ideal reporters for colorimetric detection, which generally involves an analyte-triggered alteration of aggregation degree of applied nanoparticles, and thus the change of colloidal color. However, these aggregation-based colorimetric probe are associated with a number of drawbacks, including poor stability of nanoaggregates, requirement of complicated functionalization and non-linearity of output signals. To address these problems, we herein employ mesoporous silica-coated gold nanorods (MS AuNRs) as novel nanocomposites for non-aggregation-based label-free colorimetric sensing relying on their chemical redox-modulated surface chemistry. In our sensing system, Hg(2+) ions are reduced to Hg(0) depositing on the surface of MS AuNPs and result in a great color change of MS AuNRs, while the subsequent introduction of S(2-) leads to a reverse process owing to the extraction of Hg(0) by S(2-). The experimental results for colorimetric sensing of Hg(2+) and S(2-) imply considerable sensitivity and specificity, suggesting the high potential of our approach for rapid environmental monitoring and bioanalysis in the future.

Sensing of transcription factor through controlled-assembly of metal nanoparticles modified with segmented DNA elements

We have developed a unique metal nanoparticle (mNPs)-based assay to detect sequence-specific interactions between transcription factor and its corresponding DNA-binding elements. This assay exploits the interparticle-distance dependent optical properties of noble mNPs as sensing element and utilizes specific protein-DNA interactions to control the dispersion status of the mNPs. The assay involves two sets of double-stranded (ds)DNA modified-mNPs, each carrying a half site segment of a functional DNA sequence for the protein of interest. Each of these half sites is designed to contain a short complementary sticky end that introduces base-pairing forces to facilitate particle aggregation and to form a transient full dsDNA sequence. The detection of specific protein-DNA binding is founded on the premise that the mixture of these two sets of dsDNA-mNPs experiences a remarkable particle aggregation under certain salt conditions; whereas the aggregation can be retarded in the presence of a specific protein that binds and stabilizes the transient full dsDNA structure and therefore introduces steric protection forces between particles. We have demonstrated the concept using estrogen receptor α and its response elements, with gold and silver NPs as the sensing platform. UV-vis spectroscopy, transmission electron spectroscopy, and dynamic light scattering measurements were conducted to provide full characterization of the particle aggregation/dispersion mechanism. Differing from most of the mNP-based colorimetric sensors that are designed based on the analyte-induced aggregation mechanism, current protein binding-stabilization sensing strategy reduces the false signals caused by unrelated particle destabilizing effects. It is expected that this assay principle can be directed toward other transcription factors by simply changing the recognition sequence to form different segmented dsDNA-mNP constructs.

Motion-based DNA detection using catalytic nanomotors

Synthetic nanomotors, which convert chemical energy into autonomous motion, hold considerable promise for diverse applications. In this paper, we show the use of synthetic nanomotors for detecting DNA and bacterial ribosomal RNA in a fast, simple and sensitive manner. The new motion-driven DNA-sensing concept relies on measuring changes in the speed of unmodified catalytic nanomotors induced by the dissolution of silver nanoparticle tags captured in a sandwich DNA hybridization assay. The concentration-dependent distance signals are visualized using optical microscopy, particularly through straight-line traces by magnetically aligned 'racing' nanomotors. This nanomotor biodetection strategy could be extended to monitor a wide range of biomolecular interactions using different motion transduction schemes, thus providing a versatile and powerful tool for detecting biological targets.

Colorimetric detection of DNA using unmodified metallic nanoparticles and peptide nucleic acid probes

We have developed a colorimetric assay for DNA detection based on the aggregation of unmodified metallic nanoparticles. Charge neutral peptide nucleic acids (PNA) are used as a "coagulant" of citrate anion-coated particles and as hybridization probe. In the absence of a complementary target DNA, free PNA molecules in solution induce aggressive particle aggregation because of the removal of charge repulsion as a result of PNA coating on nanoparticles. When a complementary DNA is present and PNA-DNA complexes are formed, the particles remain stable because the negative charges of the DNA strands in the complexes adsorbed on the particle surface ensure sufficient charge repulsions. In this method, no probe immobilization is needed and PNA-DNA hybridization occurs in a homogeneous phase. The assay results are displayed as rapidly as the changes in color and/or in UV-vis adsorption spectra of the colloidal solutions. We have validated the assay principle using gold- and silver-nanoparticles (AuNPs and AgNPs), with the involvement of a shorter (13 mer) and a longer (22 mer) probe sequences. A specific DNA can be detected in the presence of at least 10 times of interference DNA, and the detection limit is at a DNA/PNA ratio of 0.05. When NaCl is added to accelerate the particle aggregation, the selectivity is further improved, and single-base-mismatch discrimination is achieved. A two-component assay using a mixture of AuNPs and AgNPs has also been constituted, aiming to improve the result accuracy by making use of the multiple aggregation signatures from the two types of particles. For single-base-mismatch discrimination, the AgNPs offer a higher sensitivity than AuNPs by showing more obvious spectra and color alternation, and the two-component assay offers three parameters in the UV-vis adsorption spectra.

Gold-silver-alloy nanoprobes for one-pot multiplex DNA detection

A specific colorimetric DNA detection method based on oligonucleotide functionalized gold-silver-alloy nanoparticles (AuAg-alloy-nanoprobes) is presented. The AuAg-alloy-nanoprobes were then used for the specific detection of a DNA sequence from TP53-a gene involved in cancer development. The AuAg-alloy-nanoprobes were then used in combination with Au-nanoprobes for a one-pot dual-colour detection strategy that allowed for the simultaneous differential detection of two distinct target sequences. This system poses an unprecedented opportunity to explore the combined use of metal nanoparticles with different composition towards the development of a multiplex one-pot colorimetric assay for DNA detection.

Colorimetric detection of DNA, small molecules, proteins, and ions using unmodified gold nanoparticles and conjugated polyelectrolytes

We have demonstrated a novel sensing strategy employing single-stranded probe DNA, unmodified gold nanoparticles, and a positively charged, water-soluble conjugated polyelectrolyte to detect a broad range of targets including nucleic acid (DNA) sequences, proteins, small molecules, and inorganic ions. This nearly "universal" biosensor approach is based on the observation that, while the conjugated polyelectrolyte specifically inhibits the ability of single-stranded DNA to prevent the aggregation of gold-nanoparticles, no such inhibition is observed with double-stranded or otherwise "folded" DNA structures. Colorimetric assays employing this mechanism for the detection of hybridization are sensitive and convenient--picomolar concentrations of target DNA are readily detected with the naked eye, and the sensor works even when challenged with complex sample matrices such as blood serum. Likewise, by employing the binding-induced folding or association of aptamers we have generalized the approach to the specific and convenient detection of proteins, small molecules, and inorganic ions. Finally, this new biosensor approach is quite straightforward and can be completed in minutes without significant equipment or training overhead.

DNA-incorporating nanomaterials in biotechnological applications

The recently developed ability to controllably connect biological and inorganic objects on a molecular scale opens a new page in biomimetic methods with potential applications in biodetection, tissue engineering, targeted therapeutics and drug/gene delivery. Particularly in the biodetection arena, a rapid development of new platforms has largely been stimulated by a spectrum of novel nanomaterials with physical properties that offer efficient, sensitive and inexpensive molecular sensing. Recently, DNA-functionalized nano-objects have emerged as a new class of nanomaterials that can be controllably assembled in predesigned structures. Such DNA-based nanoscale structures might provide a new detection paradigm due to their regulated optical, electrical and magnetic responses, chemical heterogeneity and high local biomolecular concentration. The specific biorecognition DNA and its physical-chemical characteristics allows for an exploitation of DNA-functionalized nanomaterials for sensing of nucleic acids, while a broad tunability of DNA interactions permits extending their use for detection of proteins, small molecules and ions. We discuss the progress that was achieved in the last decade in the exploration of new detection methods based on DNA-incorporating nanomaterials as well as their applications to gene delivery. The comparison between various detection platforms, their sensitivity and selectivity, and specific applications are reviewed.

Surface modification, functionalization and bioconjugation of colloidal inorganic nanoparticles

Inorganic colloidal nanoparticles are very small, nanoscale objects with inorganic cores that are dispersed in a solvent. Depending on the material they consist of, nanoparticles can possess a number of different properties such as high electron density and strong optical absorption (e.g. metal particles, in particular Au), photoluminescence in the form of fluorescence (semiconductor quantum dots, e.g. CdSe or CdTe) or phosphorescence (doped oxide materials, e.g. Y(2)O(3)), or magnetic moment (e.g. iron oxide or cobalt nanoparticles). Prerequisite for every possible application is the proper surface functionalization of such nanoparticles, which determines their interaction with the environment. These interactions ultimately affect the colloidal stability of the particles, and may yield to a controlled assembly or to the delivery of nanoparticles to a target, e.g. by appropriate functional molecules on the particle surface. This work aims to review different strategies of surface modification and functionalization of inorganic colloidal nanoparticles with a special focus on the material systems gold and semiconductor nanoparticles, such as CdSe/ZnS. However, the discussed strategies are often of general nature and apply in the same way to nanoparticles of other materials.