Scanning Electron-Raman Cryomicroscopy for Characterization of Nanoparticle-Albumin Drug Products.

Nanomaterials have expanded the use of active pharmaceutical ingredients by improving efficacy, decreasing toxicity, and facilitating targeted delivery. To systematically achieve this goal, nanomaterial-containing drugs need to be manufactured with precision in attributes such as size, morphology, surface chemistry, and composition. Their physicochemical characterization is essential as their attributes govern pharmacokinetics yet can be challenging due to the nature of many nanomaterial-based formulations unless advanced sample fixation and in vitro characterization methods are utilized. Here, different cryogenic and other fixation strategies were assessed, and a novel physicochemical characterization method was developed using scanning electron Raman cryo-microscopy (SERCM). A complex nanoparticle albumin bound paclitaxel (nab-paclitaxel) formulation was chosen as a model drug. Plunge freezing (PF), high pressure freezing (HPF), freeze substitution (FS), and membrane filtration were compared for their influence on size and morphology measurements, and formulation-based variations were quantified. SERCM was introduced as a multiattribute physicochemical characterization platform, and the composition of nanoparticles was confirmed as albumin-paclitaxel complexes. By coupling image-based quantitative analysis with chemical analysis, SERCM has the potential to pave the way for the development of comprehensive tools for assessing injectable and ophthalmic nanomaterial-containing drugs in their native-like state.

Old Polymorph, New Technique: Assessing Ritonavir Crystallinity Using Low-Frequency Raman Spectroscopy.

Two decades ago, postmarket discovery of a second crystal form of ritonavir with lower solubility had major implications for drug manufacturers and patients. Since then, ritonavir has been reformulated via the hot-melt-extrusion process in an amorphous form. Here, quantitative low- and mid-frequency Raman spectroscopy methods were developed to characterize polymorphs, form I and form II, in commercial ritonavir 100 mg oral tablets as an alternate analysis approach compared to X-ray powder diffraction (XRPD). Crystallization in three lots of ritonavir products obtained from four separate manufacturers was assessed after storage under accelerated conditions at 40 °C and 75% relative humidity (RH). Results were compared with quantitative XRPD methods developed and validated according to ICH Q2 (R1) guidelines. In a four-week open-dish study, form I crystallization occurred in two of the four products and form II crystallization was detected in another ritonavir product. The limits of detection for XRPD, low-frequency Raman (LFR), and mid-frequency Raman (MFR) were determined to be 0.7, 0.8, and 0.5% for form I and 0.6, 0.6, and 1% for form II, respectively. Root-mean-squared-error of predictions were 0.6-1.0 and 0.6-2.5% for LFR- and MFR-based partial least-squares models. Further, ritonavir polymorphs could also be identified and detected directly from ritonavir tablets using transmission LFR. In summary, LFR was applied for the assessment of polymorphism in real-world samples. While providing analytical performance similar to conventional techniques, LFR reduced the single measurement time from 66 min (XRPD) to 10 s (LFR) without the need for tedious sample preparation procedures.

A Real-Time NMR Method for Measurement of In Vitro Aggregation Kinetics Of Degarelix Drug Products.

Degarelix is a gonadotropin-releasing hormone (GnRH) receptor antagonist. Upon contact with physiological fluid, degarelix undergoes quick gelation and forms a depot at the site of injection providing sustained release. The molecular gelling kinetics is a critical physiochemical quality attribute of degarelix products that may impact drug delivery. However, high-resolution and drug substance (DS)-specific analytical methods for characterizing gelling kinetics of degarelix are still lacking. Accordingly, the current study focused on developing NMR-based methods to characterize in vitro initial aggregation of degarelix in Firmagon® drug product (DP). The high-precision real-time NMR method was demonstrated to quickly differentiate lot to lot differences in degarelix aggregation kinetics, and to reveal the effects of degarelix concentration, pH, salt, and temperature on the kinetics. The results could be useful for quality assurance of degarelix products and facilitate complex generic drug development. The real-time NMR method developed here could also be adopted to other complex DPs that have varied aggregation and release properties.

Raman mapping of fentanyl transdermal delivery systems with off-label modifications.

Raman mapping is a powerful and emerging tool in characterization of pharmaceuticals and provides non-destructive chemical and structural identification with minimal sample preparation. One pharmaceutical form that is suitable but has not been studied in-depth with Raman mapping is transdermal delivery systems (TDS). TDS are dosage forms designed to deliver a therapeutically effective amount of active pharmaceutical ingredient (API) across a patient's skin. To enhance drug delivery through the skin, the API in the formulation is often close to a saturated or supersaturated state. Thus, improper use or off-label modifications can lead to occurrence of unwanted API changes, specifically, crystallization over time. Here, off-label modifications were mimicked on a set of fentanyl drug-in-adhesive TDS sold on the U.S. market by four different manufacturers via die cutting, and then the die cut TDS were investigated through confocal Raman mapping for structural and chemical changes. Using Multivariate Curve Resolution (MCR), not only was morphological and chemical characterization of transdermal systems provided, but also fentanyl crystals in certain products due to off-label modifications were identified. The chemometric model used in analysis of Raman maps allowed precise identification of fentanyl as the crystalline material as confirmed by the hit-quality-index correlation of component spectra from the chemometric model with library spectra of a fentanyl reference standard. The results show that confocal Raman mapping with MCR can be utilized in assessing pharmaceutical quality of TDS. This method has the potential to be widely used in characterization of such systems as an alternative to existing techniques.

Chiral modes and directional lasing at exceptional points.

Controlling the emission and the flow of light in micro- and nanostructures is crucial for on-chip information processing. Here we show how to impose a strong chirality and a switchable direction of light propagation in an optical system by steering it to an exceptional point (EP)-a degeneracy universally occurring in all open physical systems when two eigenvalues and the corresponding eigenstates coalesce. In our experiments with a fiber-coupled whispering-gallery-mode (WGM) resonator, we dynamically control the chirality of resonator modes and the emission direction of a WGM microlaser in the vicinity of an EP: Away from the EPs, the resonator modes are nonchiral and laser emission is bidirectional. As the system approaches an EP, the modes become chiral and allow unidirectional emission such that by transiting from one EP to another one the direction of emission can be completely reversed. Our results exemplify a very counterintuitive feature of non-Hermitian physics that paves the way to chiral photonics on a chip.

Highly sensitive detection of nanoparticles with a self-referenced and self-heterodyned whispering-gallery Raman microlaser.

Optical whispering-gallery-mode resonators (WGMRs) have emerged as promising platforms for label-free detection of nano-objects. The ultimate sensitivity of WGMRs is determined by the strength of the light-matter interaction quantified by quality factor/mode volume, Q/V, and the resolution is determined by Q. To date, to improve sensitivity and precision of detection either WGMRs have been doped with rare-earth ions to compensate losses and increase Q or plasmonic resonances have been exploited for their superior field confinement and lower V. Here, we demonstrate, for the first time to our knowledge, enhanced detection of single-nanoparticle-induced mode splitting in a silica WGMR via Raman gain-assisted loss compensation and WGM Raman microlaser. In particular, the use of the Raman microlaser provides a dopant-free, self-referenced, and self-heterodyned scheme with a detection limit ultimately determined by the thermorefractive noise. Notably, we detected and counted individual nanoparticles with polarizabilities down to 3.82 × 10(-6) µm(3) by monitoring a heterodyne beatnote signal. This level of sensitivity is achieved without exploiting plasmonic effects, external references, or active stabilization and frequency locking. Single nanoparticles are detected one at a time; however, their characterization by size or polarizability requires ensemble measurements and statistical averaging. This dopant-free scheme retains the inherited biocompatibility of silica and could find widespread use for sensing in biological media. The Raman laser and operation band of the sensor can be tailored for the specific sensing environment and the properties of the targeted materials by changing the pump laser wavelength. This scheme also opens the possibility of using intrinsic Raman or parametric gain for loss compensation in other systems where dissipation hinders progress and limits applications.

Raman gain induced mode evolution and on-demand coupling control in whispering-gallery-mode microcavities.

Waveguide-coupled optical resonators have played an important role in a wide range of applications including optical communication, sensing, nonlinear optics, slow/fast light, and cavity QED. In such a system, the coupling regimes strongly affect the resonance feature in the light transmission spectra, and hence the performance and outcomes of the applications. Therefore it is crucial to control the coupling between the waveguide and the microresonator. In this work, we investigated a fiber-taper coupled whispering-gallery-mode microresonator system, in which the coupling regime is traditionally controlled by adjusting the distance between the resonator and the fiber-taper mechanically. We propose and experimentally demonstrate that by utilizing Raman gain one can achieve on-demand control of the coupling regime without any mechanical movement in the resonator system. Particularly, the application of Raman gain is accompanied by Q enhancement. We also show that with the help of Raman gain control, the transitions between various coupling regimes can affect the light transmission spectra so as to provide better resolvability and signal amplification. This all-optical approach is also suitable for monolithically integrated and packaged waveguide-resonator systems, whose coupling regime is fixed at the time of manufacturing. It provides an effective route to control the light transmission in a waveguide-couple resonator system without mechanically moving individual optical components.

A top-down spectroscopic approach for correlating coating thickness distributions with the dissolution profiles of enterically coated pellets.

Pharmaceutical dosage forms such as tablets and capsules are often coated with a functional polymer to modify the drug release. To obtain the drug release profiles, ensure quality control and predict in-vivo performance, dissolution studies are performed. However, dissolution tests are time-consuming, sample destructive and do not readily allow for at-line or in-line characterization. Rapid assessment of functional coatings is essential for products where a single capsule is comprised of hundreds of functionally-coated pellets and the collective drug release kinetics of the entire capsule depends on contributions from each pellet. Here, single Raman measurements were used to evaluate the coating thickness distributions of a dosage form comprised of small, functionally-coated pellets in capsules. First, the composition and physicochemical properties of pellets were characterized by multivariate analysis assisted Raman mapping of pellet cross-sections. Second, a method of collecting single Raman spectrum with spectral contributions from the coating and API layers was developed and optimized to estimate the thickness of coatings. The coating thicknesses obtained from single Raman measurements of pellets in each capsule revealed thickness distributions that correlated with the dissolution profiles (capsules with one distribution had single stage release and capsules with two distributions had a two-stage release). Finally, an unsupervised multivariate analysis method was demonstrated as a rapid and efficient way to correlate dissolution profiles of enterically coated pellets. In summary, this study presents a non-destructive and rapid characterization method for assessing coating thickness and has the potential to be applied in process analytical technologies to ensure coating uniformity and predict product dissolution rate performance.

Quality of New Domestic Hand Sanitizer Drug Product Manufacturers During COVID-19.

The FDA initiated a cross-sectional, statistically based sampling and testing study to characterize the quality of marketed alcohol-based hand sanitizer (ABHS) by evaluating the alcohol content and impurities present in ABHS products manufactured by establishments that registered with the FDA during March-April 2020. A stratified sampling design divided the population of manufacturers into independent groups based on each establishment's level of experience with FDA oversight and its geographic location. ABHS products were collected and analyzed by spatially offset Raman spectroscopy and gas chromatography with mass spectrometry (GC-MS). The GC-MS results for 310 products, from 196 newly registered domestic manufacturers, showed that 71.6% (± 5.7%) of these manufacturers had violative products. In 104 (33.5%) cases, the alcohol content did not meet label claim assay specifications but still fell within CDC efficacy ranges. Ethanol ABHS products failed more often overall (assay and impurities) (84.3%) and for impurities (84.3%), than isopropanol ABHS products (11.2% and 6.2%, respectively). Differences in test results across active ingredients were statistically significant. Ethanol ABHS products often (63.5% of cases) failed due to the presence of acetal or acetaldehyde, particularly in products with pH ≤ 6. Other impurities were also detected in several ABHS products, suggesting the use of low-grade alcohol in the manufacture of these products. Evidence was insufficient to conclude that having experience manufacturing FDA-regulated products, or lack thereof, influenced product-level violative results. This study highlights the importance of sourcing and testing active pharmaceutical ingredients to produce quality drug products.

In Situ Grown Gold Nanoisland-Based Chemiresistive Electronic Nose for Sniffing Distinct Odor Fingerprints.

Chemiresistors based on metal-insulator-metal structures are attractive transducers for rapid tracing of a wide repertoire of (bio)chemical species in the vapor phase. However, current fabrication techniques suffer greatly from sensor-to-sensor variability, limiting their reproducible and reliable application in real-world settings. We demonstrate a novel, facile, and ubiquitously applicable strategy for fabricating highly reliable and reproducible organothiol-functionalized gold nanoisland-based chemiresistors. The novel fabrication technique involves iterative in situ seeding, growth, and surface functionalization of gold nanoislands on an interdigitated electrode, which in turn generates a multi-layered densely packed continuous gold nanoisland film. The chemiresistors fabricated using the proposed strategy exhibited high sensor-to-sensor reproducibility owing to the controlled iterative seeding and growth-based fabrication technique, long-term stability, and specificity for detection and identification of a wide variety of volatile organic compounds. Upon exposure to a specific odor, the chemiresistor ensemble comprised nine different chemical functionalities and produced a unique and discernable odor fingerprint that is reproducible for at least up to 90 days. Integrating these odor fingerprints with a simple linear classifier was found to be sufficient for discriminating between all six odors used in this study. We believe that the fabrication strategy presented here, which is agnostic to chemical functionality, enables fabrication of highly reliable and reproducible sensing elements, and thereby an adaptable electronic nose for a wide variety of real-world gas sensing applications.

Physicochemical and structural evaluation of microparticles in tretinoin topical gels.

Drug release from microparticle-based topical gels may affect their bioavailability, safety and efficacy. This work sought to elucidate spatial distribution of the drug within the microparticle matrix and how this impacts the product's critical performance attributes. The purpose of this research was to inform the development of in vitro characterization approaches to support a demonstration of bioequivalence. Drug-free microparticles were loaded with tretinoin or drug-loaded microparticles were separated from purchased Retin-A Micro® (tretinoin) topical gel drug products. The resultant microparticles were analyzed for tretinoin content, drug loading efficiency, morphology, surface topography, surface pore size distribution, particle size distribution and tretinoin release. The solid-state characteristics and chemical interaction of tretinoin with the microparticles were also investigated. Microparticles loaded with tretinoin made in-house and those separated from Retin-A Micro® (tretinoin) topical gel were spherical, polydisperse and free of aggregates. The surface porosity of the microparticles was ∼19.8% with an average pore size of ∼327 nm. Microparticles loaded with tretinoin in-house were smaller in size and exhibited faster drug release than those separated from Retin-A Micro® (tretinoin) topical gel. Tretinoin release was found to increase with an increase in the drug loading. Based on XRD and DSC data, tretinoin was present in an amorphous state. The FTIR spectra indicated a disappearance of carbonyl band of microparticles and shifting of the hydroxyl band of tretinoin due to hydrogen bonding. The extent of drug loading and the solid-state interaction of tretinoin with the microparticles may be critical for drug release. Additional characterization of the drug products is necessary to understand the effect of the factors examined in this work on the bioavailability and efficacy of tretinoin gels.

Through-container quantitative analysis of hand sanitizers using spatially offset Raman spectroscopy.

The COVID-19 pandemic created an increased demand for hygiene supplies such as hand sanitizers. In response, a large number of new domestic or imported hand sanitizer products entered the US market. Some of these products were later found to be out of specification. Here, to quickly assess the quality of the hand sanitizer products, a quantitative, through-container screening method was developed for rapid and non-destructive screening. Using spatially offset Raman spectroscopy (SORS) and support vector regression (SVR), active ingredients (e.g., type of alcohol) of 173 commercial and in-house products were identified and quantified regardless of the container material or opacity. Alcohol content in hand sanitizer formulations were predicted with high accuracy [Formula: see text] using SVR and [Formula: see text] of the substandard test samples were identified. In sum, a SORS-SVR method was developed and used for testing medical countermeasures used against COVID-19, demonstrating a potential for high-volume testing during public health threats.

In Vitro Testing of Sunscreens for Dermal Absorption: A Platform for Product Selection for Maximal Usage Clinical Trials.

Sunscreen products contain UV filters as active ingredients for the protection of the skin against UVR. The US Food and Drug Administration (FDA) issued a new proposed rule in 2019 (84.FR.6204) for sunscreens and identified the need for additional safety data for certain UV filters including their dermal absorption data. Dermal absorption data reveal systemic exposure of UV filters in humans, which can be obtained from clinical maximal usage trials. FDA guidance recommends conducting in vitro skin permeation tests (IVPTs) to help select formulations for maximal usage clinical trials as IVPT results may be indicative of in vivo absorption. This case study reports in vitro methodologies used for the selection of sunscreen products for an FDA-sponsored proof-of-concept maximal usage clinical trial. An IVPT method was developed using human cadaver skin. Commercially available sunscreen products were tested to determine the skin absorption potential of common UV filters using the IVPT. All the studied sunscreen products demonstrated a certain degree of skin absorption of UV filters using IVPT, and a formulation rank order was obtained. These sunscreen products were also characterized for several formulation properties including the globule size in emulsions, which was found to be an indicator for the rank order.

Interfacing whispering-gallery microresonators and free space light with cavity enhanced Rayleigh scattering.

Whispering gallery mode resonators (WGMRs) take advantage of strong light confinement and long photon lifetime for applications in sensing, optomechanics, microlasers and quantum optics. However, their rotational symmetry and low radiation loss impede energy exchange between WGMs and the surrounding. As a result, free-space coupling of light into and from WGMRs is very challenging. In previous schemes, resonators are intentionally deformed to break circular symmetry to enable free-space coupling of carefully aligned focused light, which comes with bulky size and alignment issues that hinder the realization of compact WGMR applications. Here, we report a new class of nanocouplers based on cavity enhanced Rayleigh scattering from nano-scatterer(s) on resonator surface, and demonstrate whispering gallery microlaser by free-space optical pumping of an Ytterbium doped silica microtoroid via the scatterers. This new scheme will not only expand the range of applications enabled by WGMRs, but also provide a possible route to integrate them into solar powered green photonics.