Understanding the Role of Loss Modulus of Viscoelastic Substrates in the Evaporation Dynamics of Sessile Drops.

Viscoelastic properties of soft substrates play a crucial role in the evaporation dynamics of sessile drops. Recent studies have revealed that the modification of the viscoelastic properties of substrates changes the dynamics of the three-phase contact line, consequently affecting the evaporation behavior of sessile drops. Notably, these modifications occur without any noticeable changes to the substrate's wetting characteristics or surface topography. However, the individual role of storage (G') and loss (G″) moduli of substrates on drop evaporation dynamics remains unexplored. In this study, we investigate the evaporation dynamics of water drops on two groups of poly(dimethylsiloxane)-based viscoelastic substrates possessing either identical G' with varying G″ or identical G″ with varying G'. Our study reveals that on a substrate with constant shear modulus (G'), a reduction of an order of magnitude in loss modulus shifts the evaporation process from the constant contact radius mode to the constant contact angle mode. We hypothesize that this observed shift in behavior stems from the varying viscoelastic dissipation influenced by the plateau modulus and characteristic relaxation time of polymer gels. Our hypothesis is further supported from the observation that the evaporation process persists on the substrate with constant loss modulus (G″). Our study advances the current understanding of drop evaporation on soft substrates that may find potential applications involving soft composites, biological entities, tissue engineering, and wearable electronics.

A dual mode 'turn-on' fluorescence-Raman (SERS) response probe based on a 1H-pyrrol-3(2H)-one scaffold for monitoring H2S levels in biological samples.

Discovery of the biological signaling roles of H2S has spurred great interest in developing reliable methods for its accurate detection and quantification. As considerable variation in its levels is seen during pathological conditions such as sepsis, real-time quantification methods have relevance in diagnosis as well. Of various approaches, reaction-based probes which respond through 'off-on' fluorescence emission remain the most studied. Since the intensity of emission is related to the analyte concentration in these measurements, the presence of built-in features which provide an opportunity for internal referencing will be advantageous. In view of this, a dual mode response system that senses H2S through characteristic fluorescence and Raman (SERS) signals based on a 1H-pyrrol-3(2H)-one scaffold was developed and is the main highlight of this report. This probe offers several advantages such as fast response (<1 min), and high selectivity and sensitivity with a detection limit of ∼7 nM. Imaging of H2S in HepG2 cells, making use of the SERS signal from the thiolysis product is also demonstrated.

Evaporation driven smart patterning of microparticles on a rigid-soft composite substrate.

HYPOTHESIS: A liquid droplet on a rigid polydimethylsiloxane (PDMS) substrate exhibits a higher receding contact angle (θr), therefore, recedes earlier than its softer counterpart. The three-phase contact line of a suspension droplet on a composite rigid-soft PDMS substrate can be selectively tuned wherein the contact line recedes on the rigid substrate sooner and approaches toward the softer side, with microparticles eventually being deposited in the softer substrate region. EXPERIMENTS: A composite PDMS substrate containing soft cores of various shapes (circular and non-circular) surrounded by rigid matrices was fabricated by employing 3D printing and soft lithography. A sessile suspension droplet containing spherical microparticles was deposited on the composite substrate and evaporated under ambient conditions. The evaporation dynamics was recorded and analyzed. FINDINGS: Evaporation-induced patterning (in circular, triangular, and rectangular areas) with sizes ranging from microns to millimetres were obtained. For the first time, by varying the ratio of the rigid-soft regions in the PDMS substrate, we were able to obtain different deposition sizes and shapes from an identical droplet. Instead of using lithographically patterned substrate, our simple methodology by using 3D printing and soft lithography opened up a new avenue for patterning microparticles based on a rigid-soft composite substrate.

Dual desorption electrospray ionization-laser desorption ionization mass spectrometry on a common nanoporous alumina platform for enhanced shotgun proteomic analysis.

A gold coated nanoporous alumina surface was used for dual ionization mode mass spectrometric analysis using desorption electrospray ionization (DESI) and laser desorption ionization (LDI). DESI and LDI mass spectrometry (MS) from the nanoporous alumina surface were compared with conventional electrospray ionization (ESI) mass spectrometry and matrix assisted laser desorption ionization (MALDI) for analysis of tryptic digests of proteins. Combined use of DESI and LDI offer greater peptide coverage than either method alone and comparable peptide coverage as with dual MALDI and ESI. This dual ionization technique using a common platform with same sample spot demonstrates a potential time and cost-effective tool for improved shotgun proteomic analysis.

Andropanolide and isoandrographolide, minor diterpenoids from Andrographis paniculata: structure and X-ray crystallographic analysis.

Phytochemical investigation of the leaves of Andrographis paniculata has led to the isolation of a new labdane type diterpenoid, andropanolide (1), along with seven known diterpenoids including isoandrographolide (2), previously reported as a rearrangement product of andrographolide. The structures and stereochemistry of compounds 1 and 2 were established by X-ray crystallographic analysis.