Imprinted Polymer Nanoparticles Research Articles

Florfenicol Binding to Molecularly Imprinted Polymer Nanoparticles in Model and Real Samples.

A simple and straightforward technique for coating microplate wells with molecularly imprinted polymer nanoparticles (nanoMIPs) to develop assays similar to the enzyme-linked immunosorbent (ELISA) assay to determine and quantify florfenicol (FF) in real food samples such as liquid milk and salmon muscle is presented here. The nanoMIPs were synthesized by a solid-phase approach with an immobilized FF (template) and characterized using dynamic light scattering, a SPR-2 biosensor system and transmission electron microscopy. Immobilization of nanoMIPs was conducted by preparing a homogenous solution of FF-nanoMIPs in water mixed with polyvinyl alcohol (PVA) 0.2% (w/v) in each well of a microplate. The detection of florfenicol was achieved in competitive binding experiments with a horseradish peroxidase−florfenicol (FF–HRP) conjugate. The assay made it possible to measure FF in buffer and in real samples (liquid milk and salmon muscle) within the range of 60−80 and 90–100 ng/mL, respectively. The immobilized nanoMIPs were stored for six weeks at room temperature and at 5 °C. The results indicate good signal recovery for all FF concentrations in spiked milk samples, without any detrimental effects to their binding properties. The high affinity of nanoMIPs and the lack of a requirement for cold chain logistics make them an attractive alternative to traditional antibodies used in ELISA.

Development of Molecularly Imprinted Membranes for Selective Determination of Urinary Ultra-Trace 5-Fluorouracil as Antineoplastic Drug Used in Chemotherapy

The incidence of neoplasm has significantly increased around the world over the last decades, resulting in use of anti-neoplastic drugs and the potential for occupational exposure to these drugs. One of the most commonly used chemotherapeutic drugs for treatment of malignancies is 5-fluorouracil (5-FU). In this study, in order to develop an appropriate adsorbent for selective extraction of ultra-trace 5-fluorouracil from urine samples, molecularly imprinted membranes (MIMs) of 5-FU were prepared by encapsulating molecularly imprinted polymer nanoparticles (MIP-NPs) into the electrospun polyethylene terephthalate (PET) nanofibers. The MIP-NPs encapsulated into electrospun PET nano-fibers were prepared by precipitation polymerization technique. These MIMs were used as selective sorbents for solid-phase extraction (SPE) of ultra-trace 5-FU from different samples prior to the analysis by high performance liquid chromatography (HPLC). Central Composite Design (CCD) was used for optimization of effective parameters in sorption and desorption steps of the molecularly imprinted membrane solid phase extraction (MIMSPE). The optimum operating conditions for the proposed method were pH: 6.2, amount of sorbent: 10.3 mg and absorption time: 20.5 h, the volume of eluent: 1 mL, the composition of elution solvent: the ratio of 90.3:9.7 methanol and acetic acid, and desorption time: 1.27 h. Under these optimized conditions, the limit of detection for 5-FU by MIMSPE was 0.07 μ L-1. The recoveries of 5-FU from urine sample ranged from 92.95±3.85 to 94.85±2.85%. The proposed MIMSPE-HPLC method can potentially be applied for selective detection of 5-FU in real samples with no special sample pretreatment steps.

Towards Peptide and Protein Recognition by Antibody Mimicking Synthetic Polymers – Background, State of the Art, and Future Outlook

Antibody–peptide/protein interactions are instrumental for many processes in the pharmaceutical and biotechnology industries and as tools for biomedical and biochemical research. The recent development of molecularly imprinted polymer nanoparticles displaying antibody-like recognition of peptides and proteins offers the possibility for substituting antibodies with these robust materials for applications where the structural integrity and function of antibodies is compromised by temperature, pH, solvent, etc. The background to the development of this class of antibody-mimicking material and the state-of-the-art in their synthesis and application is presented in this review.

Preparation of magnetic molecularly imprinted polymer for dispersive solid-phase extraction of valsartan and its determination by high-performance liquid chromatography: Box-Behnken design.

In this work, core/shell magnetic molecularly imprinted polymer nanoparticles were synthesized for extraction and pre-concentration of valsartan from different samples and then it was measured with high-performance liquid chromatography. For preparation of molecularly imprinted polymer nanoparticles, Fe3 O4 nanoparticles were coated with tetraethyl orthosilicate and then functionalized with 3-(trimethoxysilyl) propyl methacrylate. In the next step, molecularly imprinted polymer nanoparticles were synthesized under reflux and distillation conditions via polymerization of methacrylic acid, valsartan (as a template), azobisisobutyronitrile and ethylene glycol dimethacrylate as cross linking. The properties of molecularly imprinted polymer nanoparticle were investigated by FTIR spectroscopy, field emission scanning electron microscopy, and X-ray diffraction. Box-Behnken design with the aid of desirability function was used for optimizing the effect of variables such as the amounts of molecularly imprinted polymer nanoparticles, time of sonication, pH, and volume of methanol on the extraction percentage of valsartan. According to the obtained results, the affecting variables extraction condition were set as 10mg of adsorbent, 16min for sonication, pH=5.5 and 0.6mL methanol. The obtained linear response (r2 >0.995) was in the range of 0.005-10 µg/mL with detection limit 0.0012 µg/mLand extraction recovery was in the range of 92-95% with standard deviation less than 6% (n=3).

Co-precipitation method to prepare molecularly imprinted fluorescent polymer nanoparticles for paracetamol sensing

In recent years, molecularly imprinted polymer have attracted intensive interests owing to its abundant tailor-made recognition sites, which show high affinity and specificity toward template molecules. Herein, we reported the synthesis of paracetamol (PCM) imprinted fluorescent polymer nanoparticles through a simple co-precipitation method using commercial starting materials, followed by acidifying and washing steps to remove the templates. The fluorescence intensity of the obtained PCM imprinted nanoparticles could be quantitatively quenched by re-binding with PCM. Its efficient sensing behavior on PCM was demonstrated with a linear working range from 10 μM to 100 μM and a detection limit of 1 μM. Moreover, its accurate assay on PCM content in commercial tablets proved it a promising and reliable chemosensor for PCM sensing. Furthermore, the reported preparation only consists of co-precipitation and washing steps under mild conditions, which is a simple, cost-, time-, and energy-saving tactic to develop various kinds of molecularly imprinted polymer nanoparticles.

Molecularly Imprinted Polymer Nanoparticles for Selective Solid Phase Extraction of Fluvoxamine in Human Urine and Plasma.

In this work, the molecularly imprinted polymer nanoparticles (MIP-NPs) for the selective determination of fluvoxamine have been described. The polymer nanoparticles were synthesized by the polymerization of methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a cross-linker, 2,2-azobisisobutyronitrile as an initiator and fluvoxamine as a template molecule. The MIP-NPs were characterized using techniques that included Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). Imprinted fluvoxamine molecules were removed from the polymeric structure using acetonitrile in methanol (2:8; v/v) as the eluting solvent. The linear dynamic range for fluvoxamine was 10-1200μgL-1. The developed method was successfully applied to the extraction of fluvoxamine in complex biological samples.

Preparation of Magnetic Molecularly Imprinted Polymer (MMIP) Nanoparticles (NPs) for the Selective Extraction of Tetracycline from Milk

Core-shell magnetic molecularly imprinted polymer nanoparticles (MMIP NPs) were prepared for the adsorption and the isolation of tetracycline from food matrices. The obtained MMIP NPs were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffractometry, vibrating sample magnetometry, and thermogravimetric analysis. The adsorption properties of the MMIP NPs were systematically characterized by static, kinetic, and selective adsorption as well as reusability measurements. The MMIP NPs were shown to provide a high adsorption capacity, with a maximum value of 40.48 mg/g, satisfactory selectivity with an imprinting factor equal to 2.55, and direct magnetic separation. Moreover, the MMIP NPs were successfully applied to extract tetracycline from milk samples. Satisfactory recoveries from 91.14 to 104.52% were obtained.

Chemical Antibody Mimics Inhibit Cadherin-Mediated Cell-Cell Adhesion: A Promising Strategy for Cancer Therapy.

One of the most promising strategies to treat cancer is the use of therapeutic antibodies that disrupt cell-cell adhesion mediated by dysregulated cadherins. The principal site where cell-cell adhesion occurs encompasses Trp2 found at the N-terminal region of the protein. Herein, we employed the naturally exposed highly conserved peptide Asp1-Trp2-Val3-Ile4-Pro5-Pro6-Ile7, as epitope to prepare molecularly imprinted polymer nanoparticles (MIP-NPs) to recognize cadherins. Since MIP-NPs target the site responsible for adhesion, they were more potent than commercially available therapeutic antibodies for inhibiting cell-cell adhesion in cell aggregation assays, and for completely disrupting three-dimensional tumor spheroids as well as inhibiting invasion of HeLa cells. These biocompatible supramolecular anti-adhesives may potentially be used as immunotherapeutic or sensitizing agents to enhance antitumor effects of chemotherapy.

Chemical Antibody Mimics Inhibit Cadherin‐Mediated Cell–Cell Adhesion: A Promising Strategy for Cancer Therapy

AbstractOne of the most promising strategies to treat cancer is the use of therapeutic antibodies that disrupt cell–cell adhesion mediated by dysregulated cadherins. The principal site where cell–cell adhesion occurs encompasses Trp2 found at the N‐terminal region of the protein. Herein, we employed the naturally exposed highly conserved peptide Asp1‐Trp2‐Val3‐Ile4‐Pro5‐Pro6‐Ile7, as epitope to prepare molecularly imprinted polymer nanoparticles (MIP‐NPs) to recognize cadherins. Since MIP‐NPs target the site responsible for adhesion, they were more potent than commercially available therapeutic antibodies for inhibiting cell–cell adhesion in cell aggregation assays, and for completely disrupting three‐dimensional tumor spheroids as well as inhibiting invasion of HeLa cells. These biocompatible supramolecular anti‐adhesives may potentially be used as immunotherapeutic or sensitizing agents to enhance antitumor effects of chemotherapy.

Preparation of deep eutectic solvent-based hexagonal boron nitride-molecularly imprinted polymer nanoparticles for solid phase extraction of flavonoids.

Hexagonal boron nitride (h-BN) is introduced as a 2D scaffold during the preparation of molecularly imprinted polymers (MIPs). The MIPs were prepared from deep eutectic solvents (DES) or fromDES containing h-BN, crosslinking agent (ethylene glycoldimethacrylate), initiator (AIBN), porogen (methanol), and template (quercetin). The recognition site of the monomer is protected by the hydrogen bond of the DES before the MIP is polymerized. The formation of the final MIP was analyzed theoretically using density-functional theory. The nanoparticles were characterized by scanning electron microscopy, nitrogen sorption analysis, thermogravimetry and Fourier transform infrared spectroscopy. The introduction of h-BN resulted in an increase in the surface area of the nanoparticles. They were applied as a solid phase extraction sorbent for the extraction of flavonoids (specifically of quercetin, isorhamnetin and kaempferol) from Ginkgo biloba leaves. Following extraction with ethanol, they were quantified by HPLC. The new sorbent has distinctly improved recognition capability for flavonoids compared to conventional MIP nanoparticles. Graphical abstractDeep eutectic solvent (DES)-based molecularly imprinted polymer (MIP) was polymerized on the surface of hexagonal boron nitride (h-BN). The h-BN-MIP nanoparticles were applied as a solid phase extraction sorbent for the specific recognition of flavonoids.

Fluorescent Nanoparticles Synthesized by Carbon-Nitride-Stabilized Pickering Emulsion Polymerization for Targeted Cancer Cell Imaging.

Graphitic carbon nitride (CN) has been found to possess amphiphilic properties, enabling it to act as a solid emulsifier to stabilize the Pickering emulsion and subsequent polymerization. Herein, we used CN-stabilized Pickering emulsion polymerization to prepare molecularly imprinted polymer nanoparticles, which showed selective binding toward cancer cells. Taking advantage of its intrinsic amphiphilicity and emission properties, CN served as both the emulsifier in the polymerization process and emissive probe for cellular imaging application. Sialic acid (SA), as an important indicator of some certain cancers, was introduced into the polymer nanoparticles by forming reversible bonds with 4-vinylphenylboronic acid comonomer and removed by adjusting the pH value. The obtained SA-imprinted polymer nanoparticles exhibited good biocompatibility and excellent targeted imaging of DU 145 cells, which are prostate cancer cells having an SA-overexpressed surface. This work provides an easy, low-cost, low-toxicity, and large-scale strategy to prepare various functional polymer nanoparticles.

Thermal Detection of Cardiac Biomarkers Heart-Fatty Acid Binding Protein and ST2 Using a Molecularly Imprinted Nanoparticle-Based Multiplex Sensor Platform.

This manuscript describes the production of molecularly imprinted polymer nanoparticles (nanoMIPs) for the cardiac biomarkers heart-fatty acid binding protein (H-FABP) and ST2 by solid-phase synthesis, and their use as synthetic antibodies in a multiplexed sensing platform. Analysis by surface plasmon resonance (SPR) shows that the affinity of the nanoMIPs is similar to that of commercially available antibodies. The particles are coated onto the surface of thermocouples and inserted into 3D-printed flow cells of different multiplexed designs. We demonstrate that it is possible to selectively detect both cardiac biomarkers within the physiologically relevant range. Furthermore, the developed sensor platform is the first example of a multiplex format of this thermal analysis technique which enables simultaneous measurements of two different compounds with minimal cross selectivity. The format where three thermocouples are positioned in parallel exhibits the highest sensitivity, which is explained by modeling the heat flow distribution within the flow cell. This design is used in further experiments and proof-of-application of the sensor platform is provided by measuring spiked fetal bovine serum samples. Because of the high selectivity, short measurement time, and low cost of this array format, it provides an interesting alternative to traditional immunoassays. The use of nanoMIPs enables a multimarker strategy, which has the potential to contribute to sustainable healthcare by improving the reliability of cardiac biomarker testing.

Synthesis of molecularly imprinted polymer nanoparticles containing gentamicin drug as wound dressing based polyvinyl alcohol/gelatin nanofiber

ABSTRACTSkin injury provides a suitable place for growth of microorganisms. Molecularly imprinted polymer (MIP) shows a good performance in selective detection of drug molecules. Our aim is to produce an ideal wound dressing and to reduce the duration of treatment. For production of wound dressing, MIP was synthesized by gentamycin template. The loading and release of gentamycin were also studied. Polyvinyl alcohol (PVA)/gelatin/MIP wound dressing was electrospun. Then, to investigate the wound healing in rats, three defects with the diameters of 8 mm were created and the process was investigated at different times. Based on SEM images, the size of MIP nanoparticles was 25 nm. Drug release was also examined which gradually reached to 98% after 110 hrs. MTT assay results showed no significant cytotoxicity after 72 hrs. The results showed a significant acceleration in wound closure of samples treated by PVA/gelatin/MIP wound dressing in compare with the control group.

Highly Effective Drug Delivery and Cell Imaging Using Fluorescent Double-Imprinted Nanoparticles by Targeting Recognition of the Epitope of Membrane Protein.

Nanocarriers with both targeting ability and stable loading of drugs can more effectively deliver drugs to precise tumor sites for therapeutic effects. Accordingly, we have rationally designed fluorescent molecularly imprinted polymer nanoparticles (FMIPs), which use N-terminal epitope of P32 membrane protein as the primary template and doxorubicin (DOX) as the secondary template. The DOX imprinted cavity can stably carry the drug and the epitope-imprinted cavity allows FMIPs to actively recognize the P32-positive 4T1 cancer cells. The targeted therapeutic effect of DOX-loaded FMIPs (FMIPs@DOX) is investigated in vitro and in vivo. The FMIPs@DOX only causes apoptosis in 4T1 cancer cells compared to C8161 cells (expressing low level of P32). In addition, highly effective inhibition of 4T1 malignant breast tumors using FMIPs@DOX is achieved in the model of tumor-bearing mice. Importantly, the antitumor effect achieved by intravenous injection of FMIPs@DOX is almost identical to that by intratumoral injection. Furthermore, the FMIPs can serve as a targeted fluorescence imaging agent due to the high specificity of the epitope-imprinted cavity and the stable fluorescence of the embedded silicon nanoparticles. These results demonstrate the effectiveness of the FMIPs for active targeted drug delivery and imaging. Furthermore, the FMIPs provide a direction for drug-loaded nanocarrier.

Molecularly Imprinted Nanoparticles Assay (MINA) in Pseudo ELISA: An Alternative to Detect and Quantify Octopamine in Water and Human Urine Samples.

In 2004, octopamine was added to the list of drugs banned by the world anti-doping agency (WADA) and prohibited in any sport competition. This work aims to develop a new analytical method to detect octopamine in water and human urine samples. We proposed a pseudo-enzyme-linked immunosorbent assay (pseudo-ELISA) by replacing traditional monoclonal antibodies with molecularly imprinted polymer nanoparticles (nanoMIPs). NanoMIPs were synthesised by a solid-phase approach using a persulfate initiated polymerisation in water. Their performance was analysed in pseudo competitive ELISA based on the competition between free octopamine and octopamine-HRP conjugated. The final assay was able to detect octopamine in water within the range 1 nmol·L−1–0.1 mol·L−1 with a detection limit of 0.047 ± 0.00231 µg·mL−1 and in human urine samples within the range 1 nmol·L−1–0.0001 mol·L−1 with a detection limit of 0.059 ± 0.00281 µg·mL−1. In all experiments, nanoMIPs presented high affinity to the target molecules and almost no cross-reactivity with analogues of octopamine such as pseudophedrine or l-Tyrosine. Only slight interference was observed from the human urine matrix. The high affinity and specificity of nanoMIPs and no need to maintain a cold chain logistics makes the nanoMIPs a competitive alternative to antibodies. Furthermore, this work is the first attempt to use nanoMIPs in pseudo-ELISA assays to detect octopamine.

Epitope imprinting of Mycobacterium leprae bacteria via molecularly imprinted nanoparticles using multiple monomers approach

Mycobacterium leprae causes endemic disease leprosy which becomes chronic if not treated timely. To expedite this ‘timely diagnosis’, and that also at an early stage, here an attempt is made to fabricate an epitope-imprinted sensor. A molecularly imprinted polymer nanoparticles modified electrochemical quartz crystal microbalance sensor was developed for sensing of Mycobacterium leprae bacteria through its epitope sequence. Multiple monomers, 3-sulphopropyl methacrylate potassium salt, benzyl methacrylate and 4-aminothiophenol were utilized to imprint this bacterial epitope. Imprinted nanoparticles were electropolymerized on gold coated quartz electrode. The sensor was able to show specific binding towards the blood samples of infected patients, even in the presence of ‘matrix’ and other plasma proteins such as albumin and globulin. Even other peptide sequences, similar to epitope sequences only with two amino acid mismatches were also unable to show any binding. Sensor withstood analytical tests viz. selectivity, specificity, matrix effect, detection limit (0.161 nM), quantification limit (and 0.536 nM), reproducibility (RSD 2.01%). Hence a diagnostic tool for bacterium causing leprosy is successfully fabricated in a facile manner which will broaden the clinical access and efficient population screening can be made feasible.

A novel CuFe2O4 nanospheres molecularly imprinted polymers modified electrochemical sensor for lysozyme determination

A selective and sensitive electrochemical sensor was proposed on the basis of a nanostructured magnetic molecularly imprinted polymer (CuFe2O4-MIP) modified glassy carbon electrode (GCE) for the electrochemical detection of lysozyme. CuFe2O4 nanospheres with porous structure have been prepared via a hydrothermal method. Surface imprinting was employed to prepare molecularly imprinted polymer nanoparticles on the CuFe2O4 nanosphere surface. The synthesized magnetic nanoparticles (CuFe2O4-MNPs) and CuFe2O4-MIP were characterized with High-Resolution Transmission Electron Microscopy (HRTEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and Vibrating Sample Magnetometer (VSM) to verify successful preparation. Then cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry were employed to test the electrochemical property of the sensor, and this sensor demonstrated high electrochemical response. The results prove that the as-synthesized CuFe2O4 nanospheres have high specific capacitance characteristics and good conductivity. Under optimal conditions, the constructed multifunctional sensor presented good linearity from 0.05 to 0.8 μg mL−1with the detection limit of 1.58 × 10−3 μg mL−1for target lysozyme. Further competitive rebinding experiments results showed that this sensing material is highly selective and sensitive for lysozyme determination, and had been successfully applied to detect target protein in complex biological samples. The presented method can be applied to the detection of trace protein in biological samples.

Highly selective extraction and voltammetric determination of the opioid drug buprenorphine via a carbon paste electrode impregnated with nano-sized molecularly imprinted polymer.

An electrochemical sensor for the opioid drug buprenorphine (BUP) is described. Molecularly imprinted polymer nanoparticles (nanoMIP) were prepared and used to modify a carbon paste electrode (CPE). The BUP-imprinted polymer was synthesized using precipitation polymerization. The resulting polymer along with multiwalled carbon nanotubes (MWCNT) was used to fabricate the modified CPE which exhibited an anodic peak at about +0.73V (vs. Ag/AgCl) for BUP. The MIP on the CPE functions as selective recognition element with an imprinting factor of 5.6. The assay consists of two-steps, viz. analyte extraction at the electrode surface and differential pulse voltammetric determination of BUP. The effects of various parameters on the electrochemical signal were optimized, and the selectivity of the modified CPE over cross reactants was studied. At optimum experimental conditions, the response is linear in the 1nM to 50μM BUP concentration range, and the detection limit is 0.6nM (at S/N = 3). This method was applied to the determination of BUP in spiked urine with acceptable relative standard deviations (3.2-4.4%). Graphical abstract Schematic representation of buprenorphine (BUP) recognition and voltammetric determination at the surface of carbon paste electrode modified with imprinted polymer and carbon nanotubes.

A highly sensitive tetracycline sensor based on a combination of magnetic molecularly imprinted polymer nanoparticles and surface plasmon resonance detection.

A method is reported for in-situ detection of the antibiotic tetracycline (TC). It is based on a combination of extraction of TC by magnetic molecularly imprinted polymers nanoparticles (MMIPs NPs) and detection by surface plasmon resonance (SPR). The TC-captured MMIPs NPs were flowed over the surface of the SPR chip that was modified with mercaptoethylamine. The SPR signal undergoes a strong increase through the use of MMIPs NPs. It increases linearly in the 5.0-100pg·mL-1 TC concentration range, and the detection limit is as low as 1.0pg·mL-1 (at S/N = 3). This method shows selectivity to TC compared with structurally analogues. In order to demonstrate the power of the method, it was applied to the analysis of milk spiked with TC. These results were validated by comparing them to those of an enzyme-linked immunoassay. The average recovery is in the range of 95.7-104.6%. Graphical abstract Schematic representation of a surface plasmon resonance assay for the sensitive determination of tetracycline in milk using the magnetic molecularly imprinted polymers nanoparticles that can extract tetracycline and amplify the SPR signal.

Preparation of Dual-Template Epitope Imprinted Polymers for Targeted Fluorescence Imaging and Targeted Drug Delivery to Pancreatic Cancer BxPC-3 Cells.

Molecularly imprinted polymers were commonly used for drug delivery. However, single-template molecularly imprinted polymers often fail to achieve both drug delivery and precise targeting. To address this issue, a dual-template molecularly imprinted polymer nanoparticle used for targeted diagnosis and drug delivery for pancreatic cancer BxPC-3 cells (FH-MIPNPs) was prepared. In the FH-MIPNPs, the 71-80 peptide of human fibroblast growth-factor-inducible 14 modified with glucose (Glu-FH) and bleomycin (BLM) were used as templates simultaneously, so that the FH-MIPNPs could load BLM and bind to the BxPC-3 cells, which overexpress human fibroblast growth-factor-inducible 14 (FN14). Targeted imaging experiments in vitro show that the FH-MIPNPs could specifically target BxPC-3 cells and that there is no targeting effect on cells without expression of FN14. In vivo antitumor experiment results demonstrated that the FH-MIPNP-loaded BLM (FH-MIPNPs/BLM) could inhibit the growth of xenografts tumor of BxPC-3 (tumor volume increased to 1.05×), which shows that FH-MIPNPs/BLM had obvious targeted therapeutic effect compared to the other three control groups of BLM, FH-NIPNPs/BLM, and physiological saline (tumor volume increased to 1.5×, 1.6×, and 2.4×, respectively). What is more, FH-MIPNPs have low biotoxicity through toxicity experiments in vitro and in vivo, which is favorable toward making molecularly imprinted polymers an effective platform for tumor-targeted imaging and therapy.