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(a−c) The schematic of the temperature-induced morphological change of the pNIPAM skin in water. (d−f) The height images and (g−i) phase images of AFM of pNIPAM chain coating on the microfiber surface; a, d, g, below 35 °C; b, e, h, above 35 °C; and c, f, i, above 42 °C (after drying).

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A non-radiation based approach based on thermoresponsive polyer coated silica microfibers has been developed. A highly thermoresponsive and bio-compatible pNIPAM was surface functionlized to conjugate to the tapered silica microfiber with waist diameter of 7.5 μm. The interfacial phase transtition of coating triggered by the LCST cause a drastic mo...

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... a highly thermoresponsive smart polymer with biocompat- ibility and nontoxity, the pNIPAM has been widely used as a promising material for temperature-modulating controlled release, 16−18 which is employed here as the coating material. The abruptly tapered silica microfiber with waist diameter of 7.5 μm ( Figure S1) was fabricated by flame-brushing technique. To conjugate to the surface of the silica microfiber, electrostatic attraction was employed in the surface functionalization as follows: the end of the pNIPAM chain was modified by amino ( Figure S2), while the surface of the silica microfiber was functionalized by hydroxyl group, and then the aminated pNIPAM was attached on the hydroxylated surface of the microfiber by electrostatic attraction, as shown in Figure ...
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... key to the ultrahigh thermal sensitivity of the thermoresponsive polymer coated microfiber thermometer is the phase transition of pNIPAM and the consequent morphological change when the temperature increases above the LCST. The LCST of our synthesized pNIPAM solution without conjugating to the silica microfiber is 31 °C, which was obtained from the temperature dependence of elastic light scattering intensity as shown in Figure S3. It was previously demonstrated that the LCST could be raised when one end of the pNIPAM chain was restricted. 19,20 Here, after being conjugated to the surface of the silica microfiber, the LCST of interfacial pNIPAM was raised to ∼35 °C, which is close to the physical temperature. As shown in Figure 2a, at temperature below 35 °C, the pNIPAM chains on the microfiber are extended, becoming well-solvated random coils which exhibit little change with increasing temperature. This was further corroborated by the atomic force microscope (AFM) images in Figure 2d and g where the morphology of pNIPAM chains presented smooth skinning on the microfiber surface. However, when temperature slightly increased to above 35 °C, the pNIPAM chains began to dehydrate (Figure 2b). Their conformation underwent a "coil−globule" transition and started to aggregate. 19 The swollen chains were dehydrated, shrunk gradually, and gave rise to collapsed microgels, wrapping on the microfiber surface. Such a dramatic phase behavior change is evidenced in Figure 2e and h. After continuous heating to 42 °C, pNIPAM chains shrunk and were further dehydrated (Figure 2c), becoming poorly solvated random coils, 21 and formed a lumpy skin on the fiber surface as shown in Figure 2f and i. During this process, water was squeezed out from the pNIPAM skin of the microfiber surface. The thickness of the pNIPAM skin on the microfiber was gradually reduced 14 until the final collapsed one with less than 50% of that of the swollen microgels. 20 Consequently, this dramatic interfacial morphology change was captured by the tapered silica microfiber because of the evanescent-field interaction. The abruptly tapered silica micro- fiber excites the higher order mode (HE 12 ) which interferes with the fundamental mode (HE 11 ) and which creates interferometric fringe in the fiber transmission spectrum. As the HE 12 mode spreads into the pNIPAM coating, it feels the change of the pNIPAM morphology, and translates it into a wavelength shift in the interference fringe. Figure 3d shows the transmission spectra of the pNIPAM coated tapered microfiber at different temperatures in the range of 30−42 °C in water. Figure 3e shows the transmission dip wavelength as a function of temperature. When the temperature was below 35 °C, the dip wavelength was insensitive to temperature. The field emission scanning electron microscope (SEM) image ( Figure 3a) reveals a smooth and even pNIPAM coating on the microfiber (the pNIPAM chains are extended, becoming well- solvated random coils and forming a smooth surface on the microfiber) at temperature below 35 °C. However, when the temperature was increased to above 35 °C, the temperature sensitivity was significantly improved to 18.74 nm/°C in the temperature range of 35−42 °C, which is 2 orders of magnitude higher than that of the typical fluorescent radiation based methods such as quantum dots of 0.1 nm/°C. 13 The SEM images illustrate an uneven surface at 35 °C (Figure 3b) and a lumpy surface on microfiber at 42 °C (Figure 3c). They prove that the pNIPAM chains undergo a drastic phase change in a physiological temperature range from 35 to 42 ...
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... key to the ultrahigh thermal sensitivity of the thermoresponsive polymer coated microfiber thermometer is the phase transition of pNIPAM and the consequent morphological change when the temperature increases above the LCST. The LCST of our synthesized pNIPAM solution without conjugating to the silica microfiber is 31 °C, which was obtained from the temperature dependence of elastic light scattering intensity as shown in Figure S3. It was previously demonstrated that the LCST could be raised when one end of the pNIPAM chain was restricted. 19,20 Here, after being conjugated to the surface of the silica microfiber, the LCST of interfacial pNIPAM was raised to ∼35 °C, which is close to the physical temperature. As shown in Figure 2a, at temperature below 35 °C, the pNIPAM chains on the microfiber are extended, becoming well-solvated random coils which exhibit little change with increasing temperature. This was further corroborated by the atomic force microscope (AFM) images in Figure 2d and g where the morphology of pNIPAM chains presented smooth skinning on the microfiber surface. However, when temperature slightly increased to above 35 °C, the pNIPAM chains began to dehydrate (Figure 2b). Their conformation underwent a "coil−globule" transition and started to aggregate. 19 The swollen chains were dehydrated, shrunk gradually, and gave rise to collapsed microgels, wrapping on the microfiber surface. Such a dramatic phase behavior change is evidenced in Figure 2e and h. After continuous heating to 42 °C, pNIPAM chains shrunk and were further dehydrated (Figure 2c), becoming poorly solvated random coils, 21 and formed a lumpy skin on the fiber surface as shown in Figure 2f and i. During this process, water was squeezed out from the pNIPAM skin of the microfiber surface. The thickness of the pNIPAM skin on the microfiber was gradually reduced 14 until the final collapsed one with less than 50% of that of the swollen microgels. 20 Consequently, this dramatic interfacial morphology change was captured by the tapered silica microfiber because of the evanescent-field interaction. The abruptly tapered silica micro- fiber excites the higher order mode (HE 12 ) which interferes with the fundamental mode (HE 11 ) and which creates interferometric fringe in the fiber transmission spectrum. As the HE 12 mode spreads into the pNIPAM coating, it feels the change of the pNIPAM morphology, and translates it into a wavelength shift in the interference fringe. Figure 3d shows the transmission spectra of the pNIPAM coated tapered microfiber at different temperatures in the range of 30−42 °C in water. Figure 3e shows the transmission dip wavelength as a function of temperature. When the temperature was below 35 °C, the dip wavelength was insensitive to temperature. The field emission scanning electron microscope (SEM) image ( Figure 3a) reveals a smooth and even pNIPAM coating on the microfiber (the pNIPAM chains are extended, becoming well- solvated random coils and forming a smooth surface on the microfiber) at temperature below 35 °C. However, when the temperature was increased to above 35 °C, the temperature sensitivity was significantly improved to 18.74 nm/°C in the temperature range of 35−42 °C, which is 2 orders of magnitude higher than that of the typical fluorescent radiation based methods such as quantum dots of 0.1 nm/°C. 13 The SEM images illustrate an uneven surface at 35 °C (Figure 3b) and a lumpy surface on microfiber at 42 °C (Figure 3c). They prove that the pNIPAM chains undergo a drastic phase change in a physiological temperature range from 35 to 42 ...
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... key to the ultrahigh thermal sensitivity of the thermoresponsive polymer coated microfiber thermometer is the phase transition of pNIPAM and the consequent morphological change when the temperature increases above the LCST. The LCST of our synthesized pNIPAM solution without conjugating to the silica microfiber is 31 °C, which was obtained from the temperature dependence of elastic light scattering intensity as shown in Figure S3. It was previously demonstrated that the LCST could be raised when one end of the pNIPAM chain was restricted. 19,20 Here, after being conjugated to the surface of the silica microfiber, the LCST of interfacial pNIPAM was raised to ∼35 °C, which is close to the physical temperature. As shown in Figure 2a, at temperature below 35 °C, the pNIPAM chains on the microfiber are extended, becoming well-solvated random coils which exhibit little change with increasing temperature. This was further corroborated by the atomic force microscope (AFM) images in Figure 2d and g where the morphology of pNIPAM chains presented smooth skinning on the microfiber surface. However, when temperature slightly increased to above 35 °C, the pNIPAM chains began to dehydrate (Figure 2b). Their conformation underwent a "coil−globule" transition and started to aggregate. 19 The swollen chains were dehydrated, shrunk gradually, and gave rise to collapsed microgels, wrapping on the microfiber surface. Such a dramatic phase behavior change is evidenced in Figure 2e and h. After continuous heating to 42 °C, pNIPAM chains shrunk and were further dehydrated (Figure 2c), becoming poorly solvated random coils, 21 and formed a lumpy skin on the fiber surface as shown in Figure 2f and i. During this process, water was squeezed out from the pNIPAM skin of the microfiber surface. The thickness of the pNIPAM skin on the microfiber was gradually reduced 14 until the final collapsed one with less than 50% of that of the swollen microgels. 20 Consequently, this dramatic interfacial morphology change was captured by the tapered silica microfiber because of the evanescent-field interaction. The abruptly tapered silica micro- fiber excites the higher order mode (HE 12 ) which interferes with the fundamental mode (HE 11 ) and which creates interferometric fringe in the fiber transmission spectrum. As the HE 12 mode spreads into the pNIPAM coating, it feels the change of the pNIPAM morphology, and translates it into a wavelength shift in the interference fringe. Figure 3d shows the transmission spectra of the pNIPAM coated tapered microfiber at different temperatures in the range of 30−42 °C in water. Figure 3e shows the transmission dip wavelength as a function of temperature. When the temperature was below 35 °C, the dip wavelength was insensitive to temperature. The field emission scanning electron microscope (SEM) image ( Figure 3a) reveals a smooth and even pNIPAM coating on the microfiber (the pNIPAM chains are extended, becoming well- solvated random coils and forming a smooth surface on the microfiber) at temperature below 35 °C. However, when the temperature was increased to above 35 °C, the temperature sensitivity was significantly improved to 18.74 nm/°C in the temperature range of 35−42 °C, which is 2 orders of magnitude higher than that of the typical fluorescent radiation based methods such as quantum dots of 0.1 nm/°C. 13 The SEM images illustrate an uneven surface at 35 °C (Figure 3b) and a lumpy surface on microfiber at 42 °C (Figure 3c). They prove that the pNIPAM chains undergo a drastic phase change in a physiological temperature range from 35 to 42 ...
Context 5
... key to the ultrahigh thermal sensitivity of the thermoresponsive polymer coated microfiber thermometer is the phase transition of pNIPAM and the consequent morphological change when the temperature increases above the LCST. The LCST of our synthesized pNIPAM solution without conjugating to the silica microfiber is 31 °C, which was obtained from the temperature dependence of elastic light scattering intensity as shown in Figure S3. It was previously demonstrated that the LCST could be raised when one end of the pNIPAM chain was restricted. 19,20 Here, after being conjugated to the surface of the silica microfiber, the LCST of interfacial pNIPAM was raised to ∼35 °C, which is close to the physical temperature. As shown in Figure 2a, at temperature below 35 °C, the pNIPAM chains on the microfiber are extended, becoming well-solvated random coils which exhibit little change with increasing temperature. This was further corroborated by the atomic force microscope (AFM) images in Figure 2d and g where the morphology of pNIPAM chains presented smooth skinning on the microfiber surface. However, when temperature slightly increased to above 35 °C, the pNIPAM chains began to dehydrate (Figure 2b). Their conformation underwent a "coil−globule" transition and started to aggregate. 19 The swollen chains were dehydrated, shrunk gradually, and gave rise to collapsed microgels, wrapping on the microfiber surface. Such a dramatic phase behavior change is evidenced in Figure 2e and h. After continuous heating to 42 °C, pNIPAM chains shrunk and were further dehydrated (Figure 2c), becoming poorly solvated random coils, 21 and formed a lumpy skin on the fiber surface as shown in Figure 2f and i. During this process, water was squeezed out from the pNIPAM skin of the microfiber surface. The thickness of the pNIPAM skin on the microfiber was gradually reduced 14 until the final collapsed one with less than 50% of that of the swollen microgels. 20 Consequently, this dramatic interfacial morphology change was captured by the tapered silica microfiber because of the evanescent-field interaction. The abruptly tapered silica micro- fiber excites the higher order mode (HE 12 ) which interferes with the fundamental mode (HE 11 ) and which creates interferometric fringe in the fiber transmission spectrum. As the HE 12 mode spreads into the pNIPAM coating, it feels the change of the pNIPAM morphology, and translates it into a wavelength shift in the interference fringe. Figure 3d shows the transmission spectra of the pNIPAM coated tapered microfiber at different temperatures in the range of 30−42 °C in water. Figure 3e shows the transmission dip wavelength as a function of temperature. When the temperature was below 35 °C, the dip wavelength was insensitive to temperature. The field emission scanning electron microscope (SEM) image ( Figure 3a) reveals a smooth and even pNIPAM coating on the microfiber (the pNIPAM chains are extended, becoming well- solvated random coils and forming a smooth surface on the microfiber) at temperature below 35 °C. However, when the temperature was increased to above 35 °C, the temperature sensitivity was significantly improved to 18.74 nm/°C in the temperature range of 35−42 °C, which is 2 orders of magnitude higher than that of the typical fluorescent radiation based methods such as quantum dots of 0.1 nm/°C. 13 The SEM images illustrate an uneven surface at 35 °C (Figure 3b) and a lumpy surface on microfiber at 42 °C (Figure 3c). They prove that the pNIPAM chains undergo a drastic phase change in a physiological temperature range from 35 to 42 ...
Context 6
... key to the ultrahigh thermal sensitivity of the thermoresponsive polymer coated microfiber thermometer is the phase transition of pNIPAM and the consequent morphological change when the temperature increases above the LCST. The LCST of our synthesized pNIPAM solution without conjugating to the silica microfiber is 31 °C, which was obtained from the temperature dependence of elastic light scattering intensity as shown in Figure S3. It was previously demonstrated that the LCST could be raised when one end of the pNIPAM chain was restricted. 19,20 Here, after being conjugated to the surface of the silica microfiber, the LCST of interfacial pNIPAM was raised to ∼35 °C, which is close to the physical temperature. As shown in Figure 2a, at temperature below 35 °C, the pNIPAM chains on the microfiber are extended, becoming well-solvated random coils which exhibit little change with increasing temperature. This was further corroborated by the atomic force microscope (AFM) images in Figure 2d and g where the morphology of pNIPAM chains presented smooth skinning on the microfiber surface. However, when temperature slightly increased to above 35 °C, the pNIPAM chains began to dehydrate (Figure 2b). Their conformation underwent a "coil−globule" transition and started to aggregate. 19 The swollen chains were dehydrated, shrunk gradually, and gave rise to collapsed microgels, wrapping on the microfiber surface. Such a dramatic phase behavior change is evidenced in Figure 2e and h. After continuous heating to 42 °C, pNIPAM chains shrunk and were further dehydrated (Figure 2c), becoming poorly solvated random coils, 21 and formed a lumpy skin on the fiber surface as shown in Figure 2f and i. During this process, water was squeezed out from the pNIPAM skin of the microfiber surface. The thickness of the pNIPAM skin on the microfiber was gradually reduced 14 until the final collapsed one with less than 50% of that of the swollen microgels. 20 Consequently, this dramatic interfacial morphology change was captured by the tapered silica microfiber because of the evanescent-field interaction. The abruptly tapered silica micro- fiber excites the higher order mode (HE 12 ) which interferes with the fundamental mode (HE 11 ) and which creates interferometric fringe in the fiber transmission spectrum. As the HE 12 mode spreads into the pNIPAM coating, it feels the change of the pNIPAM morphology, and translates it into a wavelength shift in the interference fringe. Figure 3d shows the transmission spectra of the pNIPAM coated tapered microfiber at different temperatures in the range of 30−42 °C in water. Figure 3e shows the transmission dip wavelength as a function of temperature. When the temperature was below 35 °C, the dip wavelength was insensitive to temperature. The field emission scanning electron microscope (SEM) image ( Figure 3a) reveals a smooth and even pNIPAM coating on the microfiber (the pNIPAM chains are extended, becoming well- solvated random coils and forming a smooth surface on the microfiber) at temperature below 35 °C. However, when the temperature was increased to above 35 °C, the temperature sensitivity was significantly improved to 18.74 nm/°C in the temperature range of 35−42 °C, which is 2 orders of magnitude higher than that of the typical fluorescent radiation based methods such as quantum dots of 0.1 nm/°C. 13 The SEM images illustrate an uneven surface at 35 °C (Figure 3b) and a lumpy surface on microfiber at 42 °C (Figure 3c). They prove that the pNIPAM chains undergo a drastic phase change in a physiological temperature range from 35 to 42 ...
Context 7
... key to the ultrahigh thermal sensitivity of the thermoresponsive polymer coated microfiber thermometer is the phase transition of pNIPAM and the consequent morphological change when the temperature increases above the LCST. The LCST of our synthesized pNIPAM solution without conjugating to the silica microfiber is 31 °C, which was obtained from the temperature dependence of elastic light scattering intensity as shown in Figure S3. It was previously demonstrated that the LCST could be raised when one end of the pNIPAM chain was restricted. 19,20 Here, after being conjugated to the surface of the silica microfiber, the LCST of interfacial pNIPAM was raised to ∼35 °C, which is close to the physical temperature. As shown in Figure 2a, at temperature below 35 °C, the pNIPAM chains on the microfiber are extended, becoming well-solvated random coils which exhibit little change with increasing temperature. This was further corroborated by the atomic force microscope (AFM) images in Figure 2d and g where the morphology of pNIPAM chains presented smooth skinning on the microfiber surface. However, when temperature slightly increased to above 35 °C, the pNIPAM chains began to dehydrate (Figure 2b). Their conformation underwent a "coil−globule" transition and started to aggregate. 19 The swollen chains were dehydrated, shrunk gradually, and gave rise to collapsed microgels, wrapping on the microfiber surface. Such a dramatic phase behavior change is evidenced in Figure 2e and h. After continuous heating to 42 °C, pNIPAM chains shrunk and were further dehydrated (Figure 2c), becoming poorly solvated random coils, 21 and formed a lumpy skin on the fiber surface as shown in Figure 2f and i. During this process, water was squeezed out from the pNIPAM skin of the microfiber surface. The thickness of the pNIPAM skin on the microfiber was gradually reduced 14 until the final collapsed one with less than 50% of that of the swollen microgels. 20 Consequently, this dramatic interfacial morphology change was captured by the tapered silica microfiber because of the evanescent-field interaction. The abruptly tapered silica micro- fiber excites the higher order mode (HE 12 ) which interferes with the fundamental mode (HE 11 ) and which creates interferometric fringe in the fiber transmission spectrum. As the HE 12 mode spreads into the pNIPAM coating, it feels the change of the pNIPAM morphology, and translates it into a wavelength shift in the interference fringe. Figure 3d shows the transmission spectra of the pNIPAM coated tapered microfiber at different temperatures in the range of 30−42 °C in water. Figure 3e shows the transmission dip wavelength as a function of temperature. When the temperature was below 35 °C, the dip wavelength was insensitive to temperature. The field emission scanning electron microscope (SEM) image ( Figure 3a) reveals a smooth and even pNIPAM coating on the microfiber (the pNIPAM chains are extended, becoming well- solvated random coils and forming a smooth surface on the microfiber) at temperature below 35 °C. However, when the temperature was increased to above 35 °C, the temperature sensitivity was significantly improved to 18.74 nm/°C in the temperature range of 35−42 °C, which is 2 orders of magnitude higher than that of the typical fluorescent radiation based methods such as quantum dots of 0.1 nm/°C. 13 The SEM images illustrate an uneven surface at 35 °C (Figure 3b) and a lumpy surface on microfiber at 42 °C (Figure 3c). They prove that the pNIPAM chains undergo a drastic phase change in a physiological temperature range from 35 to 42 ...
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... and Characterization. The materials and characterization is provided in the Supporting Information. Briefly, aminated pNIPAM (NH 2 -pNIPAM) was prepared following our previous work 19 (as shown in Figure S2) and was dissolved in diluted water to form a ...

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