Optical tweezers with fluorescence detection for temperature-dependent microrheological measurements

Abstract

We introduce a setup of optical tweezers, capable of carrying out temperature-dependent rheological measurements of soft materials. In our setup, the particle displacement is detected by imaging a bright spot due to fluorescence emitted from a dye-labeled particle against a dark background onto a quadrant photodiode. This setup has a relatively wide space around the sample that allows us to further accessorize the optical tweezers by a temperature control unit. The applicability of the setup was examined on the basis of the rheological measurements using a typical viscoelastic system, namely a worm-like micelle solution. The temperature and frequency dependences of the local viscoelastic functions of the worm-like micelle solution obtained by this setup were in good accordance with those obtained by a conventional oscillatory rheometer, confirming the capability of the optical tweezers as a tool for the local rheological measurements of soft materials. Since the optical tweezers measurements only require a tiny amount of sample (~40 μL), the rheological measurements using our setup should be useful for soft materials of which the available amount is limited.

Mucus Microrheology Measured on Human Bronchial Epithelium Culture

“…Once an isolated bead is trapped with a laser, typical experiments consist in applying a small sinusoidal displacement either to the trap or to the sample. The motion of the bead then gives information about the viscoelastic properties of the matrix at the driving frequency ω [15][16][17]. We consider now a displacement of the stage x s * = A s e jωt (with A s the amplitude of the stage displacement) and a fixed trap.…”

“…In the linear regime, a bead of radius a follows the sinusoidal displacement with a phase shift ϕ, and its trajectory is given by x b * = A b e jωt e −jϕ (with A b the amplitude of the bead displacement). Following the analysis by Shundo et al [17] and other authors, the complex shear modulus G * = G ′ + jG ′′ is related to the ratio of the fluid forces acting on the bead to its displacement with respect to the fluid (taking into account a 6πa factor for a spherical bead). The fluid forces being opposed by the restoring harmonic force of the trap of stiffness k OT , one gets:…”

Spatial Heterogeneity Accompanying Gel Formation of Poly(N-isopropylacrylamide) Aqueous Solution at a Temperature below Cloud Point

“…The temperature of the sample was controlled by a modified setup previously reported (see the Supporting Information). , The actual temperature in the solution was monitored by a thermocouple thermometer (0.2 × 1P K-2-G-J2, Ninomiya Electric Wire Co., Ltd.). After heating to the desired temperatures of 294 and 302 K, the samples were left undisturbed for a period of 3 h prior to observation.…”

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

“…A direct fluorescence imaging was reported, wherein the particle displacement is detected by imaging a fluorescent spot of a dye‐labeled particle against a dark background onto a quadrant photodiode. It avoids the focuses of both the trapping and detection lasers on the same spot with a high precision.…”

“…For an equilibrium system, the fluctuation–dissipation theorem (FDT) guarantees that these two methods are equivalent . In this review, we will detail these two classes of microrheometers, including their basic principles and typical setups as well as some recently developed hybrid microrheometers, often used in characterizing polymer solutions and biological materials.…”